Method and apparatus for motion vector determination in video encoding or decoding

ABSTRACT

The motion vector determining method involves determining a candidate motion vector list comprising motion vectors of a plurality of candidate blocks referred so as to predict a motion vector of a current block, when a reference image of a first candidate block from among the plurality of candidate blocks is different from a reference image of the current block, determining whether or not to use a motion vector of the first candidate block from the candidate motion vector list, based on whether each of the reference image of the current block and the reference image of the first candidate block is a short-term reference image or a long-term reference image, and determining the motion vector of the current block by using a candidate motion vector selected from among the motion vectors comprised in the candidate motion vector list.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/357,043, filed on May 8, 2014 in the U.S. Patentand Trademark Office, which is a National Stage application under 35U.S.C. § 371 of International Application No. PCT/KR2012/009408, filedon Nov. 8, 2012, which claims the benefit of U.S. ProvisionalApplication No. 61/557,133, filed on Nov. 8, 2011 in the U.S. Patent andTrademark Office, the disclosures of which are incorporated herein intheir entirety by reference.

TECHNICAL FIELD

The present invention relates to video encoding and decoding, and moreparticularly, to video encoding and decoding in which inter predictionand/or motion compensation is performed.

BACKGROUND ART

As hardware for reproducing and storing high resolution or high qualityvideo content is being developed and supplied, a need for a video codecfor effectively encoding or decoding the high resolution or high qualityvideo content is increasing. According to a conventional video codec, avideo is encoded according to a limited encoding method based on amacroblock having a predetermined size.

Image data of a spatial region is transformed into coefficients of afrequency region via frequency transformation. According to a videocodec, an image is split into blocks having a predetermined size,discrete cosine transformation (DCT) is performed for each respectiveblock, and frequency coefficients are encoded in block units, for rapidcalculation of frequency transformation. Compared with image data of aspatial region, coefficients of a frequency region are easilycompressed. In particular, since an image pixel value of a spatialregion is expressed according to a prediction error via inter predictionor intra prediction of a video codec, when frequency transformation isperformed on the prediction error, a large amount of data may betransformed to 0. According to a video codec, an amount of data may bereduced by replacing data that is consecutively and repeatedly generatedwith small-sized data.

According to a multi-view video code, a base view video and one or moreadditional view videos are encoded and decoded. By removingtemporal/spatial redundancy between the base view video and theadditional view video and redundancy between views, an amount of data ofthe base view video and the additional view video can be reduced.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

The present invention provides a motion vector determining method andapparatus performed via motion vector prediction, a method and apparatusfor encoding a video by performing inter prediction and motioncompensation via motion vector prediction, and a method and apparatusfor decoding a video by performing motion compensation via motion vectorprediction.

Technical Solution

According to an aspect according to the present invention, there isprovided a motion vector determining method for inter prediction, themotion vector determining method including operations of determining acandidate motion vector list comprising motion vectors of a plurality ofcandidate blocks referred so as to predict a motion vector of a currentblock; when a reference image of a first candidate block from among theplurality of candidate blocks is different from a reference image of thecurrent block, determining whether or not to use a motion vector of thefirst candidate block from the candidate motion vector list, based onwhether each of the reference image of the current block and thereference image of the first candidate block is a short-term referenceimage or a long-term reference image; and determining the motion vectorof the current block by using a candidate motion vector selected fromamong the motion vectors comprised in the candidate motion vector list.

Advantageous Effects

When a method of determining a motion vector according to one or moreembodiments of the present invention is performed, in a case where areference image indicated by a reference index of a candidate block isdifferent from a reference image of a current block, and at least one ofthe reference images of the current block and the candidate block is along-term reference image, it is possible to skip a process of scaling asize of a motion vector of the candidate block or a process of referringto the motion vector of the candidate block, and is possible to controlthe current block to refer to a motion vector of another candidate blockhaving a relatively high prediction accuracy, whereby an efficiency of amotion vector prediction process may be improved.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a motion vector determining apparatusaccording to an embodiment according to the present invention.

FIG. 2 is a flowchart of a motion vector determining method, accordingto an embodiment of the present invention.

FIG. 3 illustrates an example in which a candidate block is a collocatedblock of another image, according to an embodiment of the presentinvention.

FIG. 4 illustrates an example in which the candidate block is aneighboring block of the same image, according to an embodiment of thepresent invention.

FIG. 5 is a flowchart of a video encoding method including the motionvector determining method, according to an embodiment of the presentinvention.

FIG. 6 is a flowchart of a video decoding method including the motionvector determining method, according to an embodiment of the presentinvention.

FIG. 7 is a block diagram of a video encoding unit including the motionvector determining apparatus, according to an embodiment of the presentinvention.

FIG. 8 is a block diagram of a video decoding unit including the motionvector determining apparatus, according to an embodiment of the presentinvention.

FIG. 9 is a block diagram of a video encoding apparatus based on acoding unit according to a tree structure, according to an embodimentaccording to the present invention.

FIG. 10 is a block diagram of a video decoding apparatus based on acoding unit according to a tree structure, according to an embodimentaccording to the present invention.

FIG. 11 is a diagram for describing a concept of coding units accordingto an embodiment according to the present invention.

FIG. 12 is a block diagram of an image encoder based on coding units,according to an embodiment according to the present invention.

FIG. 13 is a block diagram of an image decoder based on coding units,according to an embodiment according to the present invention.

FIG. 14 is a diagram illustrating deeper coding units according todepths, and partitions, according to an embodiment according to thepresent invention.

FIG. 15 is a diagram for describing a relationship between a coding unitand transformation units, according to an embodiment according to thepresent invention.

FIG. 16 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an embodiment according tothe present invention.

FIG. 17 is a diagram of deeper coding units according to depths,according to an embodiment according to the present invention.

FIGS. 18 through 20 are diagrams for describing a relationship betweencoding units, prediction units, and transformation units, according toan embodiment according to the present invention.

FIG. 21 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to encoding mode information of Table 1.

FIG. 22 illustrates a physical structure of a disc that stores aprogram, according to an embodiment of the present invention.

FIG. 23 illustrates a disc drive that records and reads a program byusing a disc.

FIG. 24 illustrates an entire structure of a content supply system thatprovides content distribution service.

FIGS. 25 and 26 illustrate external and internal structures of a mobilephone to which a video encoding method and a video decoding method areapplied, according to embodiments of the present invention.

FIG. 27 illustrates a digital broadcasting system employing acommunication system, according to an embodiment of the presentinvention.

FIG. 28 illustrates a network structure of a cloud computing systemusing a video encoding apparatus and a video decoding apparatus,according to an embodiment of the present invention.

BEST MODE

According to an aspect according to the present invention, there isprovided a motion vector determining method for inter prediction, themotion vector determining method including operations of determining acandidate motion vector list comprising motion vectors of a plurality ofcandidate blocks referred so as to predict a motion vector of a currentblock; when a reference image of a first candidate block from among theplurality of candidate blocks is different from a reference image of thecurrent block, determining whether or not to use a motion vector of thefirst candidate block from the candidate motion vector list, based onwhether each of the reference image of the current block and thereference image of the first candidate block is a short-term referenceimage or a long-term reference image; and determining the motion vectorof the current block by using a candidate motion vector selected fromamong the motion vectors comprised in the candidate motion vector list.

The first candidate block may be a neighboring block of the currentblock in a current image of the current block or may be a collocatedblock at the same position as the current block in an image that isrestored earlier than the current image.

When all of the reference image of the current block and the referenceimage of the first candidate block are the long-term reference images,the operation of determining whether or not to use the motion vector mayinclude an operation of maintaining the motion vector of the firstcandidate block in the candidate motion vector list.

When one of the reference image of the current block and the referenceimage of the first candidate block is the short-term reference image,and the other one of the reference image of the current block and thereference image of the first candidate block is the long-term referenceimage, the operation of determining whether or not to use the motionvector may include an operation of determining not to use the motionvector of the first candidate block in the candidate motion vector list.

According to another aspect according to the present invention, there isprovided a motion vector determining apparatus for inter prediction, themotion vector determining apparatus including a candidate listdetermining unit for determining a candidate motion vector listcomprising motion vectors of a plurality of candidate blocks referred soas to predict a motion vector of a current block and, when a referenceimage of a first candidate block from among the plurality of candidateblocks is different from a reference image of the current block, fordetermining whether or not to use a motion vector of the first candidateblock from the candidate motion vector list, based on whether each ofthe reference image of the current block and the reference image of thefirst candidate block is a short-term reference image or a long-termreference image; and a motion vector determining unit for determiningthe motion vector of the current block by using a candidate motionvector selected from among the motion vectors comprised in the candidatemotion vector list.

According to another aspect according to the present invention, there isprovided a computer-readable recording medium having recorded thereon acomputer program for executing the motion vector determining method.

Mode of the Invention

Hereinafter, a motion vector determining apparatus 10 and a motionvector determining method will be described with reference to FIGS. 1through 4. Also, methods and apparatuses for encoding and decoding avideo by performing the motion vector determining method will bedescribed with reference to FIGS. 5 and 8. In addition, video encodingand decoding schemes including a motion vector determining method, basedon coding units having a tree structure will be described with referenceto FIGS. 9 through 21. Hereinafter, the term ‘image’ may refer to astill image or a moving picture, that is, a video itself.

First, the motion vector determining apparatus 10 and the motion vectordetermining method will be described with reference to FIGS. 1 through4. Also, the methods and apparatuses for encoding and decoding a videoby performing the motion vector determining method will be describedwith reference to FIGS. 5 and 8. FIG. 1 is a block diagram of the motionvector determining apparatus 10 according to an embodiment according tothe present invention.

The motion vector determining apparatus 10 includes a candidate listdetermining unit 12 and a motion vector determining unit 14.

Inter prediction is performed by using a similarity between a currentimage and another image. In a reference image that is restored earlierthan the current image, a reference region that is similar to a currentregion of the current image is detected. A distance between coordinatesof the current region and the reference region is represented as amotion vector, and a difference between pixel values of the currentregion and the reference region is represented as residual data. Thus,by performing the inter prediction on the current region, it is possibleto output an index indicating the reference image, the motion vector,and the residual data, instead of directly outputting image informationabout the current region.

The motion vector determining apparatus 10 may perform the interprediction on each video image for each respective block. A block mayhave a square shape, a rectangular shape, or any geometric shape and isnot limited to a data unit having a predetermined size. According to anembodiment according to the present invention, a block may be a maximumcoding unit, a coding unit, a prediction unit, a transformation unit, orthe like from among coding units according to a tree structure. Videoencoding and decoding methods based on coding units according to a treestructure will be described below with reference to FIGS. 9 through 21.

The reference image that is used in the inter prediction of the currentimage has to be an image that is decoded earlier than the current image.In the present embodiment, the reference image for the inter predictionmay be classified into a short-term reference image and a long-termreference image. A decoded picture buffer (DPB(not shown)) storesrestored images that are generated via motion compensation on previousimages. The restored images that are previously generated may be used asthe reference image for inter prediction of other images. Thus, in orderto perform the inter prediction of the current image, at least oneshort-term reference image or at least one long-term reference image maybe selected from the restored images stored in the decoded picturebuffer. The short-term reference image may be an image that is just orrecently decoded in a decoding order including the current image,whereas the long-term reference image may be an image that is decodedmuch earlier than the current image, is selected to be used as areference image for the inter prediction of other images, and thus isstored in the decoded picture buffer.

For motion vector prediction, PU merging, or advanced motion vectorprediction (AMVP), motion vector prediction of the current block may bedetermined by referring to a motion vector of another block.

The motion vector determining apparatus 10 may determine a motion vectorby referring to a motion vector of another block that is temporally orspatially adjacent to the current block. The motion vector determiningapparatus 10 may determine a candidate motion vector list including aplurality of motion vectors of candidate blocks that may becomereference targets for the motion vector of the current block. The motionvector determining apparatus 10 may determine the motion vector of thecurrent block by referring to a motion vector selected from thecandidate motion vector list.

In the present embodiment, a candidate block may indicate a neighboringblock of the current block in the current image or may be a collocatedblock that is at the same position as the current block in an imagerestored earlier than the current image.

The candidate list determining unit 12 may scale sizes of candidatemotion vectors that satisfy a predetermined condition and that are fromthe candidate motion vector list including the motion vectors of thecandidate blocks that are referred for prediction of the motion vectorof the current block, or may exclude the candidate motion vectors fromthe candidate motion vector list.

When a reference image of a first candidate block from among thecandidate blocks included in the candidate motion vector list isdifferent from the reference image of the current block, the candidatelist determining unit 12 may determine whether each of the referenceimage of the current block and the reference image of the firstcandidate block is the short-term reference image or the long-termreference image. The candidate list determining unit 12 may determinehow to use a motion vector of the first candidate block in the candidatemotion vector list, based on whether each of the reference image of thecurrent block and the reference image of the first candidate block isthe short-term reference image or the long-term reference image.

When all of the reference image of the current block and the referenceimage of the first candidate block are the long-term reference images,the candidate list determining unit 12 may maintain the motion vector ofthe first candidate block in the candidate motion vector list. That is,the first candidate block may be included in the candidate motion vectorlist while a size of the motion vector of the first candidate block isnot scaled.

When one of the reference image of the current block and the referenceimage of the first candidate block is the short-term reference image,and the other one of the reference image of the current block and thereference image of the first candidate block is the long-term referenceimage, the candidate list determining unit 12 may determine not to usethe motion vector of the first candidate block in the candidate motionvector list. Then, the motion vector of the first candidate block may bedeclared as a non-usable motion vector.

When all of the reference image of the current block and the referenceimage of the first candidate block are the short-term reference images,the candidate list determining unit 12 may scale the size of the motionvector of the first candidate block and may include the scaled motionvector of the first candidate block in the candidate motion vector list.In this case, the candidate list determining unit 12 may scale the sizeof the motion vector of the first candidate block based on a ratio of adistance between the current image and the reference image of thecurrent block to a distance between an image of the first candidateblock and a reference image of the first candidate block, and may updatea value of the motion vector of the first candidate block as a scaledvalue in the candidate motion vector list.

The motion vector determining unit 14 may select a candidate motionvector from the motion vectors included in the candidate motion vectorlist and may determine the motion vector of the current block by usingthe selected candidate motion vector. The motion vector determining unit14 may determine the motion vector of the current block by duplicatingthe candidate motion vector without a change or by modifying thecandidate motion vector.

FIG. 2 is a flowchart of a motion vector determining method, accordingto an embodiment of the present invention.

The motion vector determining apparatus 10 may predict a motion vectorof a current block by using a motion vector of a block that istemporally or spatially close to the current block. Also, the motionvector determining apparatus 10 may determine a plurality of candidateblocks having predictable motion vectors, may select a candidate blockfrom among the candidate blocks, may refer to a motion vector of theselected candidate block, and thus may determine the motion vector ofthe current block.

However, when a reference image indicated by a reference index of acandidate block from among the candidate blocks is different from areference image of the current block, if the motion vector determiningapparatus 10 predicts the motion vector of the current block byreferring to a motion vector of the candidate block, an accuracy of thepredicted motion vector may deteriorate although a size of the motionvector of the candidate block is scaled and then the motion vector ofthe candidate block is referred to. Thus, when the reference image ofthe current block is different from the reference image of the candidateblock, the motion vector determining apparatus 10 may determine whetherto refer to the candidate block after scaling the size of the motionvector of the candidate block or may determine not to refer to thecandidate block.

Hereinafter, when the reference image of the current block is differentfrom the reference image of the candidate block, a method of predicting,by the motion vector determining apparatus 10, the motion vector of thecurrent block from the motion vector of the candidate block is describedin detail with reference to operations 21, 23, and 25.

In operation 21, the motion vector determining apparatus 10 determines acandidate motion vector list including motion vectors of a plurality ofcandidate blocks for the current block.

In operation 23, when a reference image of a first candidate block fromamong the candidate blocks is different from the reference image of thecurrent block, the motion vector determining apparatus 10 determineswhether or not to use a motion vector of the first candidate block fromthe candidate motion vector list, based on whether each of the referenceimage of the current block and the reference image of the firstcandidate block is a short-term reference image or a long-term referenceimage.

The motion vector determining apparatus 10 may determine whether thereference image of the current block is the long-term reference image,by using a long-term reference index indicating whether the referenceimage of the current block is the long-term reference image. Similarly,the motion vector determining apparatus 10 may determine whether thereference image of the first candidate block is the long-term referenceimage, by using a long-term reference index of the first candidateblock.

In another embodiment, when a value of a difference between pictureorder counts (POCs) of the reference image of the current block and thereference image of the first candidate block is greater than a firstthreshold value, the motion vector determining apparatus 10 maydetermine that the reference image of the first candidate block is thelong-term reference image. Similarly, when the value of the differencebetween the POCs of the reference image of the current block and thereference image of the first candidate block is greater than a secondthreshold value, the motion vector determining apparatus 10 maydetermine that the reference image of the current block is the long-termreference image.

In operation 25, the motion vector determining apparatus 10 determinesthe motion vector of the current block by using a candidate motionvector selected from the motion vectors included in the candidate motionvector list.

In operation 25, regardless of whether the reference image of thecurrent block is the short-term reference image or the long-termreference image, the motion vector determining apparatus 10 maydetermine a reference block indicated by the motion vector of thecurrent block that is determined in the reference image of the currentblock according to a POC indicated by a reference index of the currentblock.

In operation 23, when all of the reference image of the current blockand the reference image of the first candidate block are the long-termreference images, the motion vector determining apparatus 10 maymaintain the motion vector of the first candidate block in the candidatemotion vector list without scaling a size of the motion vector of thefirst candidate block. When one of the reference image of the currentblock and the reference image of the first candidate block is theshort-term reference image, and the other one of the reference image ofthe current block and the reference image of the first candidate blockis the long-term reference image, the motion vector determiningapparatus 10 may determine not to use the motion vector of the firstcandidate block in the candidate motion vector list. When all of thereference image of the current block and the reference image of thefirst candidate block are the short-term reference images, the motionvector determining apparatus 10 may update the motion vector of thefirst candidate block in the candidate motion vector list, according tothe motion vector of the first candidate block which is size-scaledbased on a ratio of a distance between the current image and thereference image of the current block to a distance between an image ofthe first candidate block and a reference image of the first candidateblock.

By performing operations 21, 23, and 25, the motion vector determiningapparatus 10 may re-determine the candidate motion vector list. Whenonly one of the reference image of the current block and the referenceimage of the first candidate block is the long-term reference image, themotion vector determining apparatus 10 may exclude the motion vector ofthe first candidate block from the candidate motion vector list and thusmay not use the first candidate block as a reference target. Thus, themotion vector determining apparatus 10 may determine the motion vectorof the candidate block by referring to another motion vector included inthe candidate motion vector list.

When all of the reference image of the current block and the referenceimage of the first candidate block are the long-term reference images,the motion vector determining apparatus 10 includes the motion vector ofthe first candidate block in the candidate motion vector list withoutscaling a size of the motion vector of the first candidate block. Thus,the motion vector determining apparatus 10 may select an optimalreference motion vector from among the other candidate motion vector andthe motion vector of the first candidate block included in the candidatemotion vector list and may determine the motion vector of the currentblock by using the selected reference motion vector.

When all of the reference image of the current block and the referenceimage of the first candidate block are the short-term reference images,the motion vector determining apparatus 10 may scale the size of themotion vector of the first candidate block and may include the motionvector of the first candidate block in the candidate motion vector list.Thus, the motion vector determining apparatus 10 may select an optimalreference motion vector from among the other candidate motion vector andthe size-scaled motion vector of the first candidate block included inthe candidate motion vector list and may determine the motion vector ofthe current block by using the selected reference motion vector.

Thus, according to the motion vector determining apparatus 10 and themotion vector determining method described above with reference to FIGS.1 and 2, when the reference image indicated by the reference index ofthe candidate block is different from the reference image of the currentblock, and at least one of the reference image of the current block andthe reference image of the candidate block is the long-term referenceimage, a process of scaling the size of the motion vector of thecandidate block may be skipped or a process of referring to the motionvector of the candidate block may be skipped.

That is, when the reference image of the current block is different fromthe reference image of the candidate block, and at least one of thereference image of the current block and the reference image of thecandidate block is the long-term reference image, if the motion vectorof the current block is predicted by referring to the motion vector ofthe candidate block, an accuracy of the predicted motion vector maydeteriorate, and therefore, a process of referring to the motion vectorof the candidate block, which lacks a prediction accuracy, may beskipped and the current block may be predicted by referring to a motionvector of another candidate block having a relatively high accuracy. Bydoing so, an efficiency of a motion vector prediction process may beimproved.

Hereinafter, referring to FIGS. 3 and 4, a motion vector predictingmethod according to types of a candidate block is described in detail.

FIG. 3 illustrates an example in which the candidate block is acollocated block of another image, according to an embodiment of thepresent invention.

A collocated image 35 is restored earlier than a current image 30 andmay be referred for inter prediction of a current block 31 in thecurrent image 30. The collocated image 35 may be determined according toa collocated index 32 of the current block 31.

In the collocated image 35, a block that is at the same position as thecurrent block 31 of the current image 30 may be determined as acollocated block 36. The motion vector determining apparatus 10 may usethe collocated block 36 as a candidate block, i.e., a reference targetused to predict a motion vector 34 of the current block 31. Thus, themotion vector 34 of the current block 31 may be predicted by referringto a motion vector 37 of the collocated block 36.

A collocated reference image 38 may be determined according to a POCindicated by a reference index of the collocated block 36. A currentreference image 33 may be determined according to a POC indicated by areference index of the current block 31.

However, when the collocated reference image 38 is different from thecurrent reference image 33, the motion vector determining apparatus 10may re-determine whether or not to refer to the motion vector 37 of thecollocated block 36 or how to refer to the motion vector 37 of thecollocated block 36.

In more detail, when the reference index of the collocated block 36 isdifferent from the reference index of the current block 31, the motionvector determining apparatus 10 may check whether the collocatedreference image 38 and the current reference image 33 are short-termreference images or long-term reference images, by using a long-termreference index of the collocated block 36 and a long-term referenceindex of the current block 31.

When the collocated reference image 38 is different from the currentreference image 33, the motion vector determining apparatus 10 mayre-determine whether or not to refer to the motion vector 37 of thecollocated block 36 or how to refer to the motion vector 37 of thecollocated block 36.

According to a result of the check, when the collocated reference image38 is different from the current reference image 33 but all of thecurrent reference image 33 and the collocated reference image 38 areshort-term reference images, a size of the motion vector 37 of thecollocated block 36 may be scaled based on a ratio of a distance Tdbetween the collocated image 35 and the collocated reference image 38 toa distance Tb between the current image 30 and the current referenceimage 33. Here, a distance Td between the collocated image 35 and thecollocated reference image 38 may be determined according to a value ofa difference between POCs of the collocated image 35 and the collocatedreference image 38. Similarly, the distance Tb between the current image30 and the current reference image 33 may be determined according to avalue of a difference between POCs of the current image 30 and thecurrent reference image 33.

That is, when all of the current reference image 33 and the collocatedreference image 38 are the short-term reference images, a candidatemotion vector MVcol′ may be updated by a value obtained by multiplyingthe motion vector 37 (MVcol) of the collocated block 36 by the ratio ofthe distance Td between the collocated image 35 and the collocatedreference image 38 to the distance Tb between the current image 30 andthe current reference image 33 (MVcol′=MVcol* Tb/Td).

Thus, according to the result of the check, when the collocatedreference image 38 is different from the current reference image 33 butall of the current reference image 33 and the collocated reference image38 are the short-term reference images, the motion vector determiningapparatus 10 may change the motion vector 37 of the collocated block 36as the value MVcol′ in the candidate motion vector list, wherein thevalue MVcol′ is obtained by multiplying the motion vector 37 of thecollocated block 36 by the ratio (Tb/Td) of the distance Td between thecollocated image 35 and the collocated reference image 38 to thedistance Tb between the current image 30 and the current reference image33.

When one of the current reference image 33 and the collocated referenceimage 38 is a short-term reference image, and the other one of thecurrent reference image 33 and the collocated reference image 38 is along-term reference image, a ‘NOT-AVAILABLE’ flag may be allocated tothe motion vector 37 of the collocated block 36. In this case, themotion vector 37 of the collocated block 36 may be excluded from thecandidate motion vector list.

When all of the current reference image 33 and the collocated referenceimage 38 are long-term reference images, the motion vector 37 of thecollocated block 36 may be maintained. In this case, the motion vector37 of the collocated block 36 may be maintained in the candidate motionvector list while a size of the motion vector 37 is not scaled.

FIG. 4 illustrates an example in which the candidate block is aneighboring block 46 of the same image, according to an embodiment ofthe present invention.

The motion vector determining apparatus 10 may use the neighboring block46 as a candidate block that is a reference target used in prediction ofa motion vector 44 of a current block 41, wherein the neighboring block46 is adjacent to the current block 41. Thus, the motion vector 44 ofthe current block 41 may be predicted by referring to a motion vector 47of the neighboring block 46.

A neighboring reference image 48 may be determined according to a POCindicated by a reference index of the neighboring block 46. A currentreference image 43 may be determined according to a POC indicated by areference index of the current block 41.

However, when the neighboring reference image 48 is different from thecurrent reference image 43, the motion vector determining apparatus 10may re-determine whether to refer to the motion vector 47 of theneighboring block 46 or how to refer to the motion vector 47 of theneighboring block 46.

In more detail, when the reference index of the neighboring block 46 isdifferent from the reference index of the current block 41, the motionvector determining apparatus 10 may check whether the neighboring block46 and the current reference image 43 are short-term reference images orlong-term reference images, by using the long-term reference index ofthe neighboring block 46 and the long-term reference index of thecurrent block 41.

When the neighboring reference image 48 is different from the currentreference image 43, the motion vector determining apparatus 10 mayre-determine whether to refer to the motion vector 47 of the neighboringblock 46 or how to refer to the motion vector 47 of the neighboringblock 46.

According to a result of the check, when the current reference image 43is different from the neighboring reference image 48 but all of thecurrent reference image 43 and the neighboring reference image 48 areshort-term reference images, a size of the motion vector 47 of theneighboring block 46 may be scaled based on a ratio of a distance Tdbetween a current image 40 and the neighboring reference image 48 to adistance Tb between the current image 40 and the current reference image43. The distance Td between the current image 40 and the neighboringreference image 48 may be determined as a value of a difference betweenPOCs of the current image 40 and the neighboring reference image 48.Similarly, the distance Tb between the current image 40 and the currentreference image 43 may be determined as a value of a difference betweenPOCs of the current image 40 and the current reference image 43.

That is, when all of the current reference image 43 and the neighboringreference image 48 are the short-term reference images, a candidatemotion vector MVne′ may be updated as as value obtained by multiplyingthe motion vector 47 (MVne) of the neighboring block 46 by the ratio(Tb/Td) of the distance Td between the current image 40 and theneighboring reference image 48 to the distance Tb between the currentimage 40 and the current reference image 43 (MVne′=MVne * Tb/Td).

Thus, according to the result of the check, when the current referenceimage 43 and the neighboring reference image 48 are different from eachother but all of them are the short-term reference images, the motionvector determining apparatus 10 may change the motion vector 47 of theneighboring block 46 as the value MVne′ in the candidate motion vectorlist, wherein the value MVne′ is obtained by multiplying the motionvector 47 (MVne) of the neighboring block 46 by the ratio (Tb/Td) of thedistance Td between the neighboring reference image 48 and the currentimage 40 to the distance Tb between the current image 40 and the currentreference image 43

When one of the current reference image 43 and the neighboring referenceimage 48 is a short-term reference image and the other one is along-term reference image, a ‘NON-USABLE’ flag may be allocated to themotion vector 47 of the neighboring block 46. In this case, the motionvector 47 of the neighboring block 46 may be excluded from the candidatemotion vector list of the current image 40.

When all of the current reference image 43 and the neighboring referenceimage 48 are long-term reference images, the motion vector 47 of theneighboring block 46 may be maintained. In this case, the motion vector47 of the neighboring block 46 may be maintained in the candidate motionvector list while a size of the motion vector 47 is not scaled.

In the embodiments of FIGS. 3 and 4, the motion vector determiningapparatus 10 may determine whether each of a current reference image(i.e., the current reference images 33 and 43) and a reference image(i.e., the collocated reference image 38 and the neighboring referenceimage 48) of a candidate block (i.e., the collocated block 36 and theneighboring block 46) is the short-term reference image or the long-termreference image, by using long-term reference indexes of a current block(i.e., the current blocks 31 and 41) and the candidate block, andaccording to a result of the determination, the motion vectordetermining apparatus 10 may determine whether or not to refer to amotion vector (i.e., the motion vectors 37 and 47) of the candidateblock or whether to refer to the motion vector after scaling a size ofthe motion vector.

In another embodiment, the motion vector determining apparatus 10 maydetermine whether or not to refer to the motion vector of the candidateblock or whether to refer to the motion vector after scaling the size ofthe motion vector, by using reference indexes indicating POCs of thecurrent reference image and the reference image of the candidate block,instead of using the long-term reference indexes of the current blockand the candidate block.

In more detail, the motion vector determining apparatus 10 according toanother embodiment with reference to FIG. 3 may compare a difference Trbetween the reference index of the collocated block 36 and the referenceindex of the current block 31 with a first threshold value THpocdiff1,and when the difference Tr between the reference indexes is greater thanthe first threshold value THpocdiff1, the motion vector determiningapparatus 10 may determine that the motion vector 37 of the collocatedblock 36 is not a reference target or may determine to refer to themotion vector 37 without scaling a size of the motion vector 37.

Similarly, the motion vector determining apparatus 10 according toanother embodiment with reference to FIG. 4 may compare a difference Trbetween the reference index of the neighboring block 46 and thereference index of the current block 41 with a first threshold valueTHpocdiff1, and when the difference Tr between the reference indexes isgreater than the first threshold value THpocdiff1, the motion vectordetermining apparatus 10 may determine that the motion vector 47 of theneighboring block 46 is not a reference target or may determine to referto the motion vector 47 without scaling a size of the motion vector 47.

In the other embodiments of FIGS. 3 and 4, when the difference Trbetween the reference index of the candidate block (i.e., the candidateblocks 36 and 46) and the reference index of the current block 31 isgreater than the first threshold value THpocdiff1, the motion vectordetermining apparatus 10 may determine that at least one of thecandidate reference image (i.e., the collocated reference image 38 andthe neighboring reference image 48), which is indicated by the referenceindex of the candidate block (36 and 46), and the current referenceimage (33 and 43), which is indicated by the reference index of thecurrent block 31, is the long-term reference image.

Thus, when the difference Tr between the reference index of thecandidate block (36 and 46) and the reference index of the current block31 is greater than the first threshold value THpocdiff1, the motionvector determining apparatus 10 may not need to scale the size of themotion vector (37 and 47) of the candidate block (36 and 46) by using aimage distance ratio (Tb/Td) but may determine that the candidate block(36 and 46) is not a reference target and thus may exclude the motionvector (37 and 47) of the candidate block (36 and 46) from the candidatemotion vector list. Alternatively, the motion vector determiningapparatus 10 may determine to predict the motion vector (34 and 44) ofthe current block (31 and 41) by referring to the motion vector (37 and47) of the candidate block (36 and 46) while the size of the motionvector (37 and 47) of the candidate block (36 and 46) is not scaled.

In another embodiment, the motion vector determining apparatus 10 maycompare a value of a difference between POCs of the current image (30and 40) and the current reference image (33 and 43) with a secondthreshold value THpocdiff2 and according to a result of the comparison,the motion vector determining apparatus 10 may determine whether or notto refer to the motion vector (37 and 47) of the candidate block (36 and46) or whether to refer to the scaled motion vector after scaling thesize of the motion vector (37 and 47).

Thus, when a difference Tb between the POCs of the current referenceimage (33 and 43), which is indicated by the reference index of thecurrent block (31 and 41), and the current image (30 and 40) is greaterthan the second threshold value THpocdiff2, the motion vectordetermining apparatus 10 may not need to scale the size of the motionvector (37 and 47) of the candidate block (36 and 46) by using the imagedistance ratio (Tb/Td) but may determine that the candidate block (36and 46) is not a reference target and thus may exclude the motion vector(37 and 47) of the candidate block (36 and 46) from the candidate motionvector list. Alternatively, the motion vector determining apparatus 10may determine to predict the motion vector (34 and 44) of the currentblock (31 and 41) by referring to the motion vector (37 and 47) of thecandidate block (36 and 46) while the size of the motion vector (37 and47) of the candidate block (36 and 46) is not scaled.

The first threshold value THpocdiff1 or the second threshold valueTHpocdiff2 may be set as one of values below. i) number of referenceimages; ii) double number of the number of reference images; iii) totalsum of a size of group of pictures (GOP) and the double number of thenumber of reference images; iv) total sum of maximally-allowed numbermax_num_reorder_pics of images that precede a current image in adecoding order and that are consecutive in an output order and thedouble number of the number of reference images; v) total sum of amaximum delay time max_output_delay by which an output of a restoredimage that is stored in a DPB is maximally delayed and the double numberof the number of reference images; vi) double number of the size of theGOP; vii) double number of the maximally-allowed numbermax_num_reorder_pics of images that precede the current image in thedecoding order and that are consecutive in the output order; and viii)double number of the maximum delay time max_output_delay by which theoutput of the restored image that is stored in the DPB is maximallydelayed.

When a candidate block is the collocated block 36, the first thresholdvalue THpocdiff1 or the second threshold value THpocdiff2 may varyaccording to relative positions of the current image 30, the currentreference image 33, and the collocated reference image 38. For example,there may be two cases of i) when all of the reference index of thecollocated block 36 and the reference index of the current block 31 aregreater or less than the POC of the current image 30 (first case), andii) when the POC of the current image 30 is between the reference indexof the collocated block 36 and the reference index of the current block31 (second case). The first threshold value THpocdiff1 or the secondthreshold value THpocdiff2 may differ in the first and second cases.

Also, the first threshold value THpocdiff1 or the second threshold valueTHpocdiff2 may vary based on a temporal depth of a hierarchicalstructure according to temporal prediction of the current image 30. Forexample, when a plurality of images are hierarchically referred for thetemporal prediction of the current image 30, the first threshold valueTHpocdiff1 or the second threshold value THpocdiff2 may be adjustedaccording to how many hierarchies are referred in the hierarchicalstructure.

Alternatively, the first threshold value THpocdiff1 or the secondthreshold value THpocdiff2 may vary according to a position of thecurrent image 30 in a GOP structure including the current image 30.

Alternatively, the first threshold value THpocdiff1 or the secondthreshold value THpocdiff2 may vary according to a POC of the currentimage 30 in the GOP structure including the current image 30.

The first threshold value THpocdiff1 or the second threshold valueTHpocdiff2 of the current image 30, which is used in video encoding, maybe encoded and transferred to a video decoder. For example, the firstthreshold value THpocdiff1 or the second threshold value THpocdiff2 maybe determined for each sequence, each picture, or each slice, or may beadaptively determined according to pictures. Accordingly, a sequenceparameter set (SPS), a picture parameter set (PPS), a slice header, andan adaptation parameter set (APS) may contain information about thefirst threshold value THpocdiff1 or the second threshold valueTHpocdiff2.

In another embodiment, a video encoder and the video decoder may nottransmit and receive the first threshold value THpocdiff1 or the secondthreshold value THpocdiff2 of the current image 30 but may predict thefirst threshold value THpocdiff1 or the second threshold valueTHpocdiff2. For example, the first threshold value THpocdiff1 or thesecond threshold value THpocdiff2 may be predicted based on a randomaccess or a low delay which is the hierarchical structure of thetemporal prediction of the current image 30. Alternatively, the firstthreshold value THpocdiff1 or the second threshold value THpocdiff2 maybe predicted based on the POC of the current image 30.

Hereinafter, referring to FIGS. 5 and 6, video encoding and decodingmethods including the motion vector determining method are described indetail.

FIG. 5 is a flowchart of a video encoding method including the motionvector determining method, according to an embodiment of the presentinvention.

In operation 51, according to the motion vector determining method, acandidate motion vector list including motion vectors of a plurality ofcandidate blocks that are referred so as to predict a motion vector of acurrent block may be determined.

When a reference image of a first candidate block from among thecandidate blocks is different from a reference image of the currentblock, the video encoding method may determine whether to use a motionvector of the first candidate block in the candidate motion vector listbased on whether each of the reference image of the current block andthe reference image of the first candidate block is a short-termreference image or a long-term reference image.

When all of the reference image of the current block and the referenceimage of the first candidate block are the long-term reference images,the motion vector of the first candidate block may be included in thecandidate motion vector list while a size of the motion vector of thefirst candidate block is not scaled.

When one of the reference image of the current block and the referenceimage of the first candidate block is the short-term reference image andthe other one of them is the long-term reference image, the videoencoding method may determine not to use the motion vector of the firstcandidate block in the candidate motion vector list.

When all of the reference image of the current block and the referenceimage of the first candidate block are the short-term reference images,the motion vector of the first candidate block may be included in thecandidate motion vector list after the size of the motion vector of thefirst candidate block is scaled.

In operation 53, a candidate motion vector that is determined inoperation 51 and that is from among the motion vectors included in thecandidate motion vector list may be selected as a reference motionvector, and a motion vector of the current block may be determined byreferring to the selected reference motion vector. The motion vector ofthe current block may be determined by duplicating the reference motionvector without a change or by modifying the reference motion vector. Forexample, when there is difference information about the motion vector,the reference motion vector and the difference information may besynthesized so that the motion vector of the current block may bedetermined.

When a reference block that is indicated by the motion vector of thecurrent block which is determined in the reference image of the currentblock is determined, residual data between the reference block and thecurrent block may be generated.

In operation 55, transformation and quantization may be performed on theresidual data that is generated in operation 53, so that quantizedtransform coefficients may be generated.

Inter prediction of operations 51, 53, and 55, the transformation, andthe quantization may be performed on each block of the current image, sothat the quantized transform coefficients may be generated in eachblock. Also, entropy encoding may be performed on the quantizedtransform coefficients for each block, so that a bitstream may begenerated and output.

The video encoding method according to the embodiment of FIG. 5 may beimplemented by a video encoding apparatus. A video encoding processorfor implementation of the video encoding method according to theembodiment of FIG. 5 may be mounted in the video encoding apparatus ormay drive in connection with an external video encoding apparatus, sothat the video encoding apparatus may perform video encoding operationsincluding the inter prediction, the transformation, and thequantization. According to an embodiment according to the presentinvention, an internal video encoding processor of the video encodingapparatus may be embodied by adding a video encoding processing moduleto a video encoding device, a central operating device, or a graphicoperating device as well as to a separate processor, which performs abasic video encoding operation.

FIG. 6 is a flowchart of a video decoding method including the motionvector determining method, according to an embodiment of the presentinvention.

In operation 61, a reference index and quantized transform coefficientsof a current block, and a motion vector of a candidate block may bereceived.

In operation 63, inverse-quantization and inverse-transformation may beperformed on the quantized transform coefficients of the current blockwhich are received in operation 61, so that residual data of the currentblock may be restored.

In operation 65, a candidate motion vector list for the current blockmay be determined. When a reference image of a first candidate blockfrom among a plurality of candidate blocks is different from a referenceimage of the current block, the video decoding method may determinewhether to use a motion vector of the first candidate block in thecandidate motion vector list based on whether each of the referenceimage of the current block and the reference image of the firstcandidate block is a short-term reference image or a long-term referenceimage.

When all of the reference image of the current block and the referenceimage of the first candidate block are the long-term reference images,the motion vector of the first candidate block may be included in thecandidate motion vector list while a size of the motion vector of thefirst candidate block is not scaled.

When one of the reference image of the current block and the referenceimage of the first candidate block is the short-term reference image andthe other one of them is the long-term reference image, the videodecoding method may determine not to use the motion vector of the firstcandidate block in the candidate motion vector list.

When all of the reference image of the current block and the referenceimage of the first candidate block are the short-term reference images,the motion vector of the first candidate block may be included in thecandidate motion vector list after the size of the motion vector of thefirst candidate block is scaled.

In operation 67, a candidate motion vector that is determined inoperation 65 and that is from among the motion vectors included in thecandidate motion vector list may be selected as a reference motionvector, and a motion vector of the current block may be determined byreferring to the selected reference motion vector. For example, whendifference information about the motion vector is received, thereference motion vector and the difference information may besynthesized so that the motion vector of the current block may bedetermined.

A reference block that is indicated by the motion vector of the currentblock in the reference image of the current block which is indicated bya reference index of the current block may be determined. Bysynthesizing the determined reference block and residual data of thecurrent block, the current block may be restored.

Operations 61, 63, 65, and 67 may be performed for each of blocks, sothat the current image including the restored blocks may be restored. Asimages are restored, a video including a sequence of the restored imagesmay be restored.

A video decoding procedure including operations 61, 63, 65, and 67 maybe performed when the video is restored by receiving an encoded videostream and then decoding the video stream. In this case, in operation61, the received video stream may be parsed and thus quantized transformcoefficients of the reference index of the current block, and the motionvector of the candidate block may be extracted from the video stream.

The video decoding procedure including operations 61, 63, 65, and 67 mayalso be performed to generate a restored image to be referred for interprediction of another image in the aforementioned video encoding method.In this case, in operation 61, the reference index and the quantizedtransform coefficients of the current block, which are generated via theinter prediction, the transformation, and the quantization, and themotion vector of the candidate block may be received, and thenoperations 63, 65, and 67 may be stepwise performed, so that afinally-restored current image may be used as a reference image forinter prediction of another image.

The video decoding method according to the embodiment of FIG. 6 may beimplemented by a video decoding apparatus. A video decoding processorfor implementation of the video decoding method according to theembodiment of FIG. 6 may be mounted in the video decoding apparatus ormay drive in connection with an external video decoding apparatus, sothat the video decoding apparatus may perform video decoding operationsincluding the inverse quantization, the inverse transformation, and theintra prediction, and the motion compensation. According to anembodiment according to the present invention, an internal videodecoding processor of the video decoding apparatus may be embodied byadding a video decoding processing module to a video decoding device, acentral operating device, or a graphic operating device as well as to aseparate processor, which performs a basic video decoding operation.

FIG. 7 is a block diagram of a video encoding unit 70 including themotion vector determining apparatus 10, according to an embodiment ofthe present invention.

The video encoding unit 70 includes an inter prediction unit 71 and atransformation and quantization unit 75. The inter prediction unit 71may include the motion vector determining apparatus 10 and a residualgeneration unit 73.

The motion vector determining apparatus 10 determines a motion vectorfor each block. Also, for motion vector prediction, PU merging, or AMVP,a motion vector of a current block may be predicted by referring to amotion vector of another block. The motion vector determining apparatus10 may determine a candidate motion vector list of the current block soas to perform motion vector prediction. A reference motion vector may bedecided from among candidate motion vectors included in the candidatemotion vector list.

The motion vector determining apparatus 10 may determine the referencemotion vector by selecting an optimal candidate motion vector from amongthe motion vectors included in the candidate motion vector list and maydetermine the motion vector of the current block by using the selectedreference motion vector.

The residual generation unit 73 may determine a reference block that isindicated by the motion vector of the current block in the referenceimage of the current block and may generate residual data between thereference block and the current block.

Accordingly, the inter prediction unit 71 may perform inter predictionfor each block and then may output the residual data for each block.

The transformation and quantization unit 75 may perform transformationand quantization on the residual data that is output from the interprediction unit 71 and thus may generate quantized transformcoefficients. The transformation and quantization unit 75 may performthe transformation and the quantization on the residual data for eachblock which is received from the inter prediction unit 71 and thus maygenerate the quantized transform coefficients for each block.

The video encoding unit 70 may perform entropy encoding on the quantizedtransform coefficients which are generated by the transformation andquantization unit 75 and thus may output an encoded bitstream. Also,when the reference index, the motion vector, a long-term referenceindex, or the like are output from the inter prediction unit 71, thevideo encoding unit 70 may perform the entropy encoding not only on thequantized transform coefficients but also on the reference index, themotion vector, and the long-term reference index and thus may output abitstream.

FIG. 8 is a block diagram of a video decoding unit 80 including themotion vector determining apparatus 10, according to an embodiment ofthe present invention.

The video decoding unit 80 includes an inverse-quantization andinverse-transformation unit 81 and a motion compensation unit 83. Themotion compensation unit 83 may include the motion vector determiningapparatus 10 and a block restoring unit 85.

The video decoding unit 80 may receive a reference index and quantizedtransform coefficients of a current block, and a motion vector of acandidate block. The inverse-quantization and inverse-transformationunit 81 may perform inverse quantization and inverse transformation onthe quantized transform coefficients of the current block and thus mayrestore residual data of the current block.

The motion compensation unit 83 may perform motion compensation on thecurrent block that is encoded via inter prediction and thus may restorethe current block.

The motion vector determining apparatus 10 determines a motion vectorfor each block. The motion vector determining apparatus 10 may determinea candidate motion vector list of the current block so as to predict themotion vector. A candidate block may include a collocated block or aneighboring block. The motion vector determining apparatus 10 maydetermine a reference motion vector from among candidate motion vectorsincluded in the candidate motion vector list.

When a reference image of a first candidate block from among thecandidate blocks included in the candidate motion vector list of thecurrent block is different from the reference image of the currentblock, the motion vector determining apparatus 10 may determine whetheror not to use the reference image of the first candidate block in thecandidate motion vector list, based on whether each of the referenceimage of the current block and the reference image of the firstcandidate block is a short-term reference image or a long-term referenceimage.

The motion vector determining apparatus 10 may determine the referencemotion vector by selecting an optimal candidate motion vector from amongthe candidate motion vectors included in the candidate motion vectorlist, may predict a motion vector of the current block by using thereference motion vector, and then may determine the motion vector of thecurrent block.

The block restoring unit 85 may determine the reference image of thecurrent block which is indicated by a reference index of the currentblock which is received by the video decoding unit 80. A reference blockthat the motion vector of the current block, which is determined in themotion vector determining apparatus 10, indicates in the reference imagemay be determined, the reference block and residual data of the currentblock may be synthesized, and thus the current block may be restored.

The motion compensation unit 83 may perform motion compensation for eachblock, may restore each block, and thus may restore the current imageincluding restored blocks. In this manner, the video decoding unit 80may restore images and thus may restore a video including an imagesequence.

The video decoding unit 80 may further include an in-loop filtering unit(not shown) that performs deblocking filtering on the restored imageincluding the current block and blocks which are restored as the blocksare restored.

The video decoding unit 80 may receive an encoded video stream, maydecode the video stream, and thus may restore the video. In this case,the video decoding unit 80 may parse the video stream and thus mayextract the reference index and the quantized transform coefficients ofthe current block, and the motion vector of the candidate block from thevideo stream. Also, the video decoding unit 80 may further include areceiving unit (not shown) that receives a bitstream, that performsentropy decoding on the bitstream, and that parses and extracts thereference index and the quantized transform coefficients of the currentblock, and the motion vector of the candidate block from the bitstream.

In order to generate a restored image to be referred for interprediction of another image by the video encoding unit 70 that isdescribed above with reference to FIG. 7, the video decoding unit 80 maybe combined with the video encoding unit 70. In this case, the videodecoding unit 80 may receive the reference index and the quantizedtransform coefficients of the current block, which are generated via theinter prediction, the transformation, and the quantization and then areoutput from the video encoding unit 70, may receive the motion vector ofthe candidate block, and may output the current image that is finallyrestored by the inverse-quantization and inverse-transformation unit 81and the motion compensation unit 83. The restored image that is outputfrom the video decoding unit 80 may be used as a reference image forinter prediction of another image by the video encoding unit 70.

As described above, in the motion vector determining apparatus 10,blocks obtained by splitting video data is split into coding unitsaccording to a tree structure, and prediction coding units are used forinter prediction for a coding unit. Hereinafter, with reference to FIGS.9 through 22, a method and apparatus for encoding a video and a methodand apparatus for decoding a video, based on a coding unit and atransformation unit according to a tree structure will be described.

FIG. 9 is a block diagram of a video encoding apparatus 100 based on acoding unit according to a tree structure, according to an embodimentaccording to the present invention.

The video encoding apparatus 100 via video prediction based on a codingunit according to a tree structure includes a maximum coding unitsplitting unit 110, a coding unit determiner 120 and an output unit 130.Hereinafter, for convenience of description, the video encodingapparatus 100 via video prediction based on a coding unit according to atree structure is referred to as ‘the video encoding apparatus 100’.

The maximum coding unit splitting unit 110 may split a current picturebased on a maximum coding unit for the current picture of an image. Ifthe current picture is larger than the maximum coding unit, image dataof the current picture may be split into the at least one maximum codingunit. The maximum coding unit according to an embodiment according tothe present invention may be a data unit having a size of 32×32, 64×64,128×128, 256×256, etc., wherein a shape of the data unit is a squarehaving a width and length in squares of 2. The image data may be outputto the coding unit determiner 120 by at least one maximum coding unit.

A coding unit according to an embodiment according to the presentinvention may be characterized by a maximum size and a depth. The depthdenotes a number of times the coding unit is spatially split from themaximum coding unit, and as the depth deepens, deeper encoding unitsaccording to depths may be split from the maximum coding unit to aminimum coding unit. A depth of the maximum coding unit is an uppermostdepth and a depth of the minimum coding unit is a lowermost depth. Sincea size of a coding unit corresponding to each depth decreases as thedepth of the maximum coding unit deepens, a coding unit corresponding toan upper depth may include a plurality of coding units corresponding tolower depths.

As described above, the image data of the current picture is split intothe maximum coding units according to a maximum size of the coding unit,and each of the maximum coding units may include deeper coding unitsthat are split according to depths. Since the maximum coding unitaccording to an embodiment according to the present invention is splitaccording to depths, the image data of a spatial domain included in themaximum coding unit may be hierarchically classified according todepths.

A maximum depth and a maximum size of a coding unit, which limit thetotal number of times a height and a width of the maximum coding unitare hierarchically split may be predetermined.

The coding unit determiner 120 encodes at least one split regionobtained by splitting a region of the maximum coding unit according todepths, and determines a depth to output a finally encoded image dataaccording to the at least one split region. In other words, the codingunit determiner 120 determines a coded depth by encoding the image datain the deeper coding units according to depths, according to the maximumcoding unit of the current picture, and selecting a depth having theleast encoding error. Thus, the encoded image data of the coding unitcorresponding to the determined coded depth is finally output. Also, thecoding units corresponding to the coded depth may be regarded as encodedcoding units. The determined coded depth and the encoded image dataaccording to the determined coded depth are output to the output unit130.

The image data in the maximum coding unit is encoded based on the deepercoding units corresponding to at least one depth equal to or below themaximum depth, and results of encoding the image data are compared basedon each of the deeper coding units. A depth having the least encodingerror may be selected after comparing encoding errors of the deepercoding units. At least one coded depth may be selected for each maximumcoding unit.

The size of the maximum coding unit is split as a coding unit ishierarchically split according to depths, and as the number of codingunits increases. Also, even if coding units correspond to the same depthin one maximum coding unit, it is determined whether to split each ofthe coding units corresponding to the same depth to a lower depth bymeasuring an encoding error of the image data of the each coding unit,separately. Accordingly, even when image data is included in one maximumcoding unit, the image data is split into regions according to thedepths and the encoding errors may differ according to regions in theone maximum coding unit, and thus the coded depths may differ accordingto regions in the image data. Thus, one or more coded depths may bedetermined in one maximum coding unit, and the image data of the maximumcoding unit may be divided according to coding units of at least onecoded depth.

Accordingly, the coding unit determiner 120 may determine coding unitshaving a tree structure included in the maximum coding unit. The ‘codingunits having a tree structure’ according to an embodiment according tothe present invention include coding units corresponding to a depthdetermined to be the coded depth, from among all deeper coding unitsincluded in the maximum coding unit. A coding unit of a coded depth maybe hierarchically determined according to depths in the same region ofthe maximum coding unit, and may be independently determined indifferent regions. Similarly, a coded depth in a current region may beindependently determined from a coded depth in another region.

A maximum depth according to an embodiment according to the presentinvention is an index related to the number of times splitting isperformed from a maximum coding unit to a minimum coding unit. A firstmaximum depth according to an embodiment according to the presentinvention may denote the total number of times splitting is performedfrom the maximum coding unit to the minimum coding unit. A secondmaximum depth according to an embodiment according to the presentinvention may denote the total number of depth levels from the maximumcoding unit to the minimum coding unit. For example, when a depth of themaximum coding unit is 0, a depth of a coding unit, in which the maximumcoding unit is split once, may be set to 1, and a depth of a codingunit, in which the maximum coding unit is split twice, may be set to 2.Here, if the minimum coding unit is a coding unit in which the maximumcoding unit is split four times, 5 depth levels of depths 0, 1, 2, 3 and4 exist, and thus the first maximum depth may be set to 4, and thesecond maximum depth may be set to 5.

Prediction encoding and transformation may be performed according to themaximum coding unit. The prediction encoding and the transformation arealso performed based on the deeper coding units according to a depthequal to or depths less than the maximum depth, according to the maximumcoding unit. Transformation may be performed according to a method oforthogonal transformation or integer transformation.

Since the number of deeper coding units increases whenever the maximumcoding unit is split according to depths, encoding including theprediction encoding and the transformation is performed on all of thedeeper coding units generated as the depth deepens. For convenience ofdescription, the prediction encoding and the transformation will now bedescribed based on a coding unit of a current depth, in a maximum codingunit.

The video encoding apparatus 100 may variously select a size or shape ofa data unit for encoding the image data. In order to encode the imagedata, operations, such as prediction encoding, transformation, andentropy encoding, are performed, and at this time, the same data unitmay be used for all operations or different data units may be used foreach operation.

For example, the video encoding apparatus 100 may select not only acoding unit for encoding the image data, but also a data unit differentfrom the coding unit so as to perform the prediction encoding on theimage data in the coding unit.

In order to perform prediction encoding on the maximum coding unit, theprediction encoding may be performed based on a coding unitcorresponding to a coded depth, i.e., based on a coding unit that is nolonger split into coding units corresponding to a lower depth.Hereinafter, the coding unit that is no longer split and becomes a basisunit for prediction encoding will now be referred to as a ‘predictionunit’. A partition obtained by splitting the prediction unit may includea prediction unit or a data unit obtained by splitting at least one of aheight and a width of the prediction unit. The partition is a data unitobtained by dividing the prediction unit of the coding unit and theprediction unit may be a partition having the same size as the codingunit.

For example, when a coding unit of 2N×2N (where N is a positive integer)is no longer split and becomes a prediction unit of 2N×2N, a size of apartition may be 2N×2N, 2N×N, N×2N, or N×N. Examples of a partition typeinclude symmetrical partitions that are obtained by symmetricallysplitting a height or width of the prediction unit, partitions obtainedby asymmetrically splitting the height or width of the prediction unit,such as 1:n or n:1, partitions that are obtained by geometricallysplitting the prediction unit, and partitions having arbitrary shapes.

A prediction mode of the prediction unit may be at least one of an intramode, a inter mode, and a skip mode. For example, the intra mode or theinter mode may be performed on the partition of 2N×2N, 2N×N, N×2N, orN×N. Also, the skip mode may be performed only on the partition of2N×2N. The encoding is independently performed on one prediction unit ina coding unit, thereby selecting a prediction mode having a leastencoding error.

The video encoding apparatus 100 may also perform the transformation onthe image data in a coding unit based not only on the coding unit forencoding the image data, but also based on a transformation unit that isdifferent from the coding unit. In order to perform the transformationin the coding unit, the transformation may be performed based on a dataunit having a size smaller than or equal to the coding unit. Forexample, the transformation unit for the transformation may include atransformation unit for an intra mode and a data unit for an inter mode.

Similarly to the coding unit according to the tree structure accordingto the present embodiment, the transformation unit in the coding unitmay be recursively split into smaller sized regions and residual data inthe coding unit may be divided according to the transformation havingthe tree structure according to transformation depths.

According to an embodiment according to the present invention, atransformation depth indicating the number of times splitting isperformed to reach the transformation unit by splitting the height andwidth of the coding unit may also be set in the transformation unit. Forexample, when the size of a transformation unit of a current coding unitis 2N×2N, a transformation depth may be set to 0. When the size of atransformation unit is N×N, the transformation depth may be set to 1. Inaddition, when the size of the transformation unit is N/2×N/2, thetransformation depth may be set to 2. That is, the transformation unitaccording to the tree structure may also be set according to thetransformation depth.

Encoding information according to coding units corresponding to a codeddepth requires not only information about the coded depth, but alsoabout information related to prediction encoding and transformation.Accordingly, the coding unit determiner 120 not only determines a codeddepth having a least encoding error, but also determines a partitiontype in a prediction unit, a prediction mode according to predictionunits, and a size of a transformation unit for transformation.

Coding units and a prediction unit/partition according to a treestructure in a maximum coding unit, and a method of determining atransformation unit, according to embodiments according to the presentinvention, will be described in detail later with reference to FIGS. 11through 22.

The coding unit determiner 120 may measure an encoding error of deepercoding units according to depths by using Rate-Distortion Optimizationbased on Lagrangian multipliers.

The output unit 130 outputs the image data of the maximum coding unit,which is encoded based on the at least one coded depth determined by thecoding unit determiner 120, and information about the encoding modeaccording to the coded depth, in bitstreams.

The encoded image data may be obtained by encoding residual data of animage.

The information about the encoding mode according to the coded depth mayinclude information about the coded depth, the partition type in theprediction unit, the prediction mode, and the size of the transformationunit.

The information about the coded depth may be defined by using splitinformation according to depths, which indicates whether encoding isperformed on coding units of a lower depth instead of a current depth.If the current depth of the current coding unit is the coded depth,image data in the current coding unit is encoded and output, and thusthe split information may be defined not to split the current codingunit to a lower depth. Alternatively, if the current depth of thecurrent coding unit is not the coded depth, the encoding is performed onthe coding unit of the lower depth, and thus the split information maybe defined to split the current coding unit to obtain the coding unitsof the lower depth.

If the current depth is not the coded depth, encoding is performed onthe coding unit that is split into the coding unit of the lower depth.Since at least one coding unit of the lower depth exists in one codingunit of the current depth, the encoding is repeatedly performed on eachcoding unit of the lower depth, and thus the encoding may be recursivelyperformed for the coding units having the same depth.

Since the coding units having a tree structure are determined for onemaximum coding unit, and information about at least one encoding mode isdetermined for a coding unit of a coded depth, information about atleast one encoding mode may be determined for one maximum coding unit.Also, a coded depth of the image data of the maximum coding unit may bedifferent according to locations since the image data is hierarchicallysplit according to depths, and thus information about the coded depthand the encoding mode may be set for the image data.

Accordingly, the output unit 130 may assign encoding information about acorresponding coded depth and an encoding mode to at least one of thecoding unit, the prediction unit, and a minimum unit included in themaximum coding unit.

The minimum unit according to an embodiment according to the presentinvention is a rectangular data unit obtained by splitting the minimumcoding unit constituting the lowermost depth by 4. Alternatively, theminimum unit may be a maximum rectangular data unit having a maximumsize, which is included in all of the coding units, prediction units,partition units, and transformation units included in the maximum codingunit.

For example, the encoding information output through the output unit 130may be classified into encoding information according to coding units,and encoding information according to prediction units. The encodinginformation according to the coding units may include the informationabout the prediction mode and about the size of the partitions. Theencoding information according to the prediction units may includeinformation about an estimated direction of an inter mode, about areference image index of the inter mode, about a motion vector, about achroma component of an intra mode, and about an interpolation method ofthe intra mode.

Also, information about a maximum size of the coding unit definedaccording to pictures, slices, or GOPs, and information about a maximumdepth may be inserted into a header of a bitstream, a SPS (SequenceParameter Set) or a picture parameter set (PPS).

In addition, information about a maximum size of a transformation unitand information about a minimum size of a transformation, which areacceptable for a current video may also be output via a header of abitstream, a SPS or a PPS. The output unit 130 may encode and outputreference information, prediction information, single-directionprediction information, and information about a slice type including afourth slice type, which are related to prediction described withreference to FIGS. 1 through 8.

In the video encoding apparatus 100, the deeper coding unit may be acoding unit obtained by dividing a height or width of a coding unit ofan upper depth, which is one layer above, by two. In other words, whenthe size of the coding unit of the current depth is 2N×2N, the size ofthe coding unit of the lower depth is N×N. Also, the coding unit of thecurrent depth having the size of 2N×2N may include a maximum value 4 ofthe coding unit of the lower depth.

Accordingly, the video encoding apparatus 100 may form the coding unitshaving the tree structure by determining coding units having an optimumshape and an optimum size for each maximum coding unit, based on thesize of the maximum coding unit and the maximum depth determinedconsidering characteristics of the current picture. Also, since encodingmay be performed on each maximum coding unit by using any one of variousprediction modes and transformations, an optimum encoding mode may bedetermined considering characteristics of the coding unit of variousimage sizes.

Thus, if an image having high resolution or large data amount is encodedin a conventional macroblock, a number of macroblocks per pictureexcessively increases. Accordingly, a number of pieces of compressedinformation generated for each macroblock increases, and thus it isdifficult to transmit the compressed information and data compressionefficiency decreases. However, by using the video encoding apparatus100, image compression efficiency may be increased since a coding unitis adjusted while considering characteristics of an image whileincreasing a maximum size of a coding unit while considering a size ofthe image.

The video encoding apparatus 100 of FIG. 9 may perform operations by themotion vector determining apparatus 10 and the video encoding unit 70which are described above with reference to FIG. 1.

The coding unit determiner 120 may determine a prediction unit includinga partition for inter prediction for each respective coding unitaccording to a tree structure for each maximum coding unit and mayperform inter prediction for each respective prediction unit.

The coding unit determiner 120 determines a motion vector for eachrespective prediction unit. Also, for motion vector prediction, PUmerging, or AMVP, a motion vector of a current prediction unit(partition) may be predicted by referring to a motion vector of anotherprediction unit. The coding unit determiner 120 may determine acandidate motion vector list of the current prediction unit so as toperform the motion vector prediction. A reference motion vector may bedecided from among candidate motion vectors included in the candidatemotion vector list. The first candidate prediction unit may be aneighboring prediction unit that is adjacent to the current predictionunit in a current image or may be a collocated prediction unit in acollocated image.

When a reference image of a first candidate prediction unit from amongthe candidate prediction units in the candidate motion vector list ofthe current prediction unit is different from the reference image of thecurrent prediction unit, the coding unit determiner 120 determineswhether or not to use a motion vector of the first candidate predictionunit from the candidate motion vector list, based on whether each of thereference image of the current prediction unit and the reference imageof the first candidate prediction unit is a short-term reference imageor a long-term reference image.

Alternatively, it is possible to determine whether each of the referenceimage of the current prediction unit and the reference image of thefirst candidate prediction unit is a short-term reference image or along-term reference image, based on long-term reference indexes of thecurrent prediction unit and the first candidate prediction unit.

When all of the reference image of the current prediction unit and thereference image of the first candidate prediction unit are the long-termreference images, it is possible to maintain the motion vector of thefirst candidate prediction unit in the candidate motion vector listwithout scaling a size of the motion vector of the first candidateprediction unit.

When one of the reference image of the current prediction unit and thereference image of the first candidate block is the short-term referenceimage, and the other one of the reference image of the currentprediction unit and the reference image of the first candidate block isthe long-term reference image, it is possible to determine not to usethe motion vector of the first candidate prediction unit in thecandidate motion vector list.

When all of the reference image of the current prediction unit and thereference image of the first candidate prediction unit are theshort-term reference images, it is possible to scale the size of themotion vector of the first candidate prediction unit and then to includethe motion vector of the first candidate prediction unit in thecandidate motion vector list.

The coding unit determiner 120 may determine a reference motion vectorby selecting an optimal reference motion vector from among motionvectors included in the candidate motion vector list and may predict anddetermine the motion vector of the current prediction unit by using theselected reference motion vector.

The coding unit determiner 120 may determine the reference image of thecurrent prediction unit according to a POC indicated by the referenceindex of the current prediction unit. Regardless of whether thereference image of the current prediction unit is the short-termreference image or the long-term reference image, the reference indexmay indicate the POC and the coding unit determiner 120 may determine animage, which is indicated by the POC, as the reference image.

The coding unit determiner 120 may determine a reference block that isindicated by the motion vector of the current prediction unit in thereference image of the current prediction unit and may generate residualdata between the reference prediction unit and the current predictionunit.

Accordingly, the coding unit determiner 120 may perform inter predictionfor each prediction unit and then may output the residual data for eachprediction unit.

The coding unit determiner 120 may perform transformation andquantization on transformation units of a coding unit including theresidual data for each prediction unit and thus may generate quantizedtransform coefficients. Accordingly, the coding unit determiner 120 maygenerate the quantized transform coefficients for each transformationunit.

Also, the coding unit determiner 120 may perform operations of the videodecoding unit 80 described above with reference to FIG. 8, in order togenerate a reference image used in inter prediction of a predictionunit.

The coding unit determiner 120 may perform inverse-quantization andinverse-transformation on the quantized transform coefficients of thecurrent prediction unit, and thus may restore the residual data of thecurrent block.

The coding unit determiner 120 may determine the candidate motion vectorlist of the current prediction unit, and when the reference image of thefirst candidate prediction unit from among the candidate predictionunits in the candidate motion vector list of the current prediction unitis different from the reference image of the current prediction unit,the coding unit determiner 120 may determine whether or not to use amotion vector of the first candidate prediction unit from the candidatemotion vector list, based on whether each of the reference image of thecurrent prediction unit and the reference image of the first candidateprediction unit is the short-term reference image or the long-termreference image.

The coding unit determiner 120 may determine the reference motion vectorby selecting the optimal reference motion vector from among the motionvectors included in the candidate motion vector list and may predict anddetermine the motion vector of the current prediction unit by using theselected reference motion vector.

The coding unit determiner 120 may determine the reference image of thecurrent prediction unit indicated by the reference index of the currentprediction unit. That is, the reference image of the current predictionunit may be determined according to the POC indicated by the referenceindex of the current prediction unit. Regardless of whether thereference image of the current prediction unit is the short-termreference image or the long-term reference image, the reference indexmay indicate the POC and an image that is indicated by the POC may bedetermined as the reference image.

Accordingly, the coding unit determiner 120 may perform motioncompensation for each prediction unit, may restore each prediction unit,and thus may restore the current image including the restored predictionunits. The restored prediction unit and image may become referencetargets of another prediction unit and another image.

FIG. 10 is a block diagram of a video decoding apparatus 200 based on acoding unit according to a tree structure, according to an embodimentaccording to the present invention.

The video decoding apparatus 200 based on the coding unit according tothe tree structure includes a receiver 210, an image data and encodinginformation extractor 220, and an image data decoder 230. Hereinafter,for convenience of description, the video decoding apparatus 200 usingvideo prediction based on a coding unit according to a tree structurewill be referred to as the ‘video decoding apparatus 200’.

Definitions of various terms, such as a coding unit, a depth, aprediction unit, a transformation unit, and information about variousencoding modes, for decoding operations of the video decoding apparatus200 are identical to those described with reference to FIG. 9 and thevideo encoding apparatus 100.

The receiver 210 receives and parses a bitstream of an encoded video.The image data and encoding information extractor 220 extracts encodedimage data for each coding unit from the parsed bitstream, wherein thecoding units have a tree structure according to each maximum codingunit, and outputs the extracted image data to the image data decoder230. The image data and encoding information extractor 220 may extractinformation about a maximum size of a coding unit of a current picture,from a header about the current picture, a SPS, or a PPS.

Also, the image data and encoding information extractor 220 extractsinformation about a coded depth and an encoding mode for the codingunits having a tree structure according to each maximum coding unit,from the parsed bitstream. The extracted information about the codeddepth and the encoding mode is output to the image data decoder 230. Inother words, the image data in a bit stream is split into the maximumcoding unit so that the image data decoder 230 decodes the image datafor each maximum coding unit.

The information about the coded depth and the encoding mode according tothe maximum coding unit may be set for information about at least onecoding unit corresponding to the coded depth, and information about anencoding mode may include information about a partition type of acorresponding coding unit corresponding to the coded depth, about aprediction mode, and a size of a transformation unit. Also, splittinginformation according to depths may be extracted as the informationabout the coded depth.

The information about the coded depth and the encoding mode according toeach maximum coding unit extracted by the image data and encodinginformation extractor 220 is information about a coded depth and anencoding mode determined to generate a minimum encoding error when anencoder, such as the video encoding apparatus 100, repeatedly performsencoding for each deeper coding unit according to depths according toeach maximum coding unit. Accordingly, the video decoding apparatus 200may restore an image by decoding the image data according to a codeddepth and an encoding mode that generates the minimum encoding error.

Since encoding information about the coded depth and the encoding modemay be assigned to a predetermined data unit from among a correspondingcoding unit, a prediction unit, and a minimum unit, the image data andencoding information extractor 220 may extract the information about thecoded depth and the encoding mode according to the predetermined dataunits. The predetermined data units to which the same information aboutthe coded depth and the encoding mode is assigned may be inferred to bethe data units included in the same maximum coding unit.

The image data decoder 230 restores the current picture by decoding theimage data in each maximum coding unit based on the information aboutthe coded depth and the encoding mode according to the maximum codingunits. In other words, the image data decoder 230 may decode the encodedimage data based on the extracted information about the partition type,the prediction mode, and the transformation unit for each coding unitfrom among the coding units having the tree structure included in eachmaximum coding unit. A decoding process may include prediction includingintra prediction and motion compensation, and inverse transformation.Inverse transformation may be performed according to a method of inverseorthogonal transformation or inverse integer transformation.

The image data decoder 230 may perform intra prediction or motioncompensation according to a partition and a prediction mode of eachcoding unit, based on the information about the partition type and theprediction mode of the prediction unit of the coding unit according tocoded depths.

In addition, the image data decoder 230 may read transformation unitinformation according to a tree structure for each coding unit so as todetermine transform units for each coding unit and perform inversetransformation based on transformation units for each coding unit, forinverse transformation for each maximum coding unit. Via the inversetransformation, a pixel value of a spatial region of the coding unit maybe restored.

The image data decoder 230 may determine at least one coded depth of acurrent maximum coding unit by using split information according todepths. If the split information indicates that image data is no longersplit in the current depth, the current depth is a coded depth.Accordingly, the image data decoder 230 may decode encoded data of atleast one coding unit corresponding to each coded depth in the currentmaximum coding unit by using the information about the partition type ofthe prediction unit, the prediction mode, and the size of thetransformation unit for each coding unit corresponding to the codeddepth, and output the image data of the current maximum coding unit.

In other words, data units containing the encoding information includingthe same split information may be gathered by observing the encodinginformation set assigned for the predetermined data unit from among thecoding unit, the prediction unit, and the minimum unit, and the gathereddata units may be considered to be one data unit to be decoded by theimage data decoder 230 in the same encoding mode. For each coding unitdetermined as described above, information about an encoding mode may beobtained so as to decode the current coding unit.

Also, the image data decoder 230 of the video decoding apparatus 200shown in FIG. 10 may perform operations of the motion vector determiningapparatus 10 and the video decoding unit 80 described above withreference to FIG. 1.

The image data decoder 230 may determine prediction units for motioncompensation and may perform the motion compensation on respectiveprediction units for each respective coding unit according to a treestructure in each maximum coding unit. The image data decoder 230 mayperform inverse-quantization and inverse-transformation on quantizedtransform coefficients of the current prediction unit and thus mayrestore residual data of the current block. The image data decoder 230may perform motion compensation on the current prediction unit that isencoded via inter prediction and thus may restore the current predictionunit.

The image data decoder 230 may determine a candidate motion vector listof the current prediction unit, and when a reference image of a firstcandidate prediction unit from among candidate prediction units in thecandidate motion vector list is different from a reference image of thecurrent prediction unit, the image data decoder 230 may determinewhether or not to use a motion vector of the first candidate predictionunit from the candidate motion vector list, based on whether each of thereference image of the current prediction unit and the reference imageof the first candidate prediction unit is a short-term reference imageor a long-term reference image. The first candidate prediction unit maybe a neighboring prediction unit that is adjacent to the currentprediction unit in a current image or may be a collocated predictionunit in a collocated image.

It is possible to determine whether each of the reference image of thecurrent prediction unit and the reference image of the first candidateprediction unit is a short-term reference image or a long-term referenceimage, based on long-term reference indexes of the current predictionunit and the first candidate prediction unit.

When all of the reference image of the current prediction unit and thereference image of the first candidate prediction unit are the long-termreference images, it is possible to maintain the motion vector of thefirst candidate prediction unit in the candidate motion vector listwithout scaling a size of the motion vector of the first candidateprediction unit.

When one of the reference image of the current prediction unit and thereference image of the first candidate block is the short-term referenceimage, and the other one of the reference image of the currentprediction unit and the reference image of the first candidate block isthe long-term reference image, it is possible to determine not to usethe motion vector of the first candidate prediction unit in thecandidate motion vector list.

When all of the reference image of the current prediction unit and thereference image of the first candidate prediction unit are theshort-term reference images, it is possible to scale the size of themotion vector of the first candidate prediction unit and then to includethe motion vector of the first candidate prediction unit in thecandidate motion vector list.

The image data decoder 230 may determine a reference motion vector byselecting an optimal reference motion vector from among motion vectorsincluded in the candidate motion vector list and may predict anddetermine the motion vector of the current prediction unit by using theselected reference motion vector.

The image data decoder 230 may determine the reference image of thecurrent prediction unit according to a POC indicated by the referenceindex of the current prediction unit. Regardless of whether thereference image of the current prediction unit is the short-termreference image or the long-term reference image, the reference indexmay indicate the POC and the image data decoder 230 may determine animage, which is indicated by the POC, as the reference image.

A reference prediction unit that is indicated by the motion vector ofthe current prediction unit in the reference image of the currentprediction unit may be determined, and the reference prediction unit andthe residual data of the current prediction unit may be synthesized, sothat the current prediction unit may be restored.

Accordingly, the image data decoder 230 may perform motion compensationfor each prediction unit, may restore each prediction unit, and thus mayrestore the current image including the restored prediction units. Asimages are restored in the aforementioned manner, a video including asequence of the restored images may be restored. Also, the restoredprediction unit and image may become reference targets of anotherprediction unit and another image.

The video decoding apparatus 200 may obtain information about at leastone coding unit that generates the minimum encoding error when encodingis recursively performed for each maximum coding unit, and may use theinformation to decode the current picture. In other words, the codingunits having the tree structure determined to be the optimum codingunits in each maximum coding unit may be decoded. Also, the maximum sizeof a coding unit is determined considering resolution and an amount ofimage data.

Accordingly, even if image data has high resolution and a large amountof data, the image data may be efficiently decoded and restored by usinga size of a coding unit and an encoding mode, which are adaptivelydetermined according to characteristics of the image data, by usinginformation about an optimum encoding mode received from an encoder.

FIG. 11 is a diagram for describing a concept of coding units accordingto an embodiment according to the present invention.

A size of a coding unit may be expressed in width×height, and may be64×64, 32×32, 16×16, and 8×8. A coding unit of 64×64 may be split intopartitions of 64×64, 64×32, 32×64, or 32×32 , and a coding unit of 32×32may be split into partitions of 32×32, 32×16, 16×32, or 16×16, a codingunit of 16×16 may be split into partitions of 16×16, 16×8, 8×16, or 8×8,and a coding unit of 8×8 may be split into partitions of 8×8, 8×4, 4×8,or 4×4.

In video data 310, a resolution is 1920×1080, a maximum size of a codingunit is 64, and a maximum depth is 2. In video data 320, a resolution is1920×1080, a maximum size of a coding unit is 64, and a maximum depth is3. In video data 330, a resolution is 352×288, a maximum size of acoding unit is 16, and a maximum depth is 1. The maximum depth shown inFIG. 11 denotes a total number of splits from a maximum coding unit to aminimum decoding unit.

If a resolution is high or a data amount is large, a maximum size of acoding unit may be large so as to not only increase encoding efficiencybut also to accurately reflect characteristics of an image. Accordingly,the maximum size of the coding unit of the video data 310 and 320 havingthe higher resolution than the video data 330 may be 64.

Since the maximum depth of the video data 310 is 2, coding units 315 ofthe video data 310 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32 and 16 sincedepths are deepened to two layers by splitting the maximum coding unittwice. Meanwhile, since the maximum depth of the video data 330 is 1,coding units 335 of the video data 330 may include a maximum coding unithaving a long axis size of 16, and coding units having a long axis sizeof 8 since depths are deepened to one layer by splitting the maximumcoding unit once.

Since the maximum depth of the video data 320 is 3, coding units 325 ofthe video data 320 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32, 16, and 8since the depths are deepened to 3 layers by splitting the maximumcoding unit three times. As a depth deepens, detailed information may beprecisely expressed.

FIG. 12 is a block diagram of an image encoder 400 based on codingunits, according to an embodiment according to the present invention.

The image encoder 400 performs operations of the coding unit determiner120 of the video encoding apparatus 100 to encode image data. In otherwords, an intra predictor 410 performs intra prediction on coding unitsin an intra mode, from among a current frame 405, and a motion estimator420 and a motion compensator 425 performs inter estimation and motioncompensation on coding units in an inter mode from among the currentframe 405 by using the current frame 405, and a reference frame 495.

Data output from the intra predictor 410, the motion estimator 420, andthe motion compensator 425 is output as quantized transformationcoefficients through a transformer 430 and a quantizer 440. Thequantized transformation coefficients are restored as data in a spatialdomain through an inverse quantizer 460 and an inverse transformer 470,and the restored data in the spatial domain is output as the referenceframe 495 after being post-processed through a deblocking unit 480 and aloop filtering unit 490. The quantized transformation coefficients maybe output as a bitstream 455 through an entropy encoder 450.

In order for the image encoder 400 to be applied in the video encodingapparatus 100, all elements of the image encoder 400, i.e., the intrapredictor 410, the motion estimator 420, the motion compensator 425, thetransformer 430, the quantizer 440, the entropy encoder 450, the inversequantizer 460, the inverse transformer 470, the deblocking unit 480, andthe loop filtering unit 490 perform operations based on each coding unitfrom among coding units having a tree structure while considering themaximum depth of each maximum coding unit.

Specifically, the intra predictor 410, the motion estimator 420, and themotion compensator 425 determines partitions and a prediction mode ofeach coding unit from among the coding units having a tree structurewhile considering the maximum size and the maximum depth of a currentmaximum coding unit, and the transformer 430 determines the size of thetransformation unit in each coding unit from among the coding unitshaving a tree structure.

Specifically, for motion vector prediction, PU merging, or AMVP, themotion estimator 420 may predict a motion vector of a current predictionunit (partition) by referring to a motion vector of another predictionunit.

When a reference image of a first candidate prediction unit from amongthe candidate prediction units in the candidate motion vector list ofthe current prediction unit is different from the reference frame 495 ofthe current prediction unit, the motion estimator 420 determines whetheror not to use a motion vector of the first candidate prediction unitfrom the candidate motion vector list, based on whether each of thereference frame 495 of the current prediction unit and the referenceimage of the first candidate prediction unit is a short-term referenceimage or a long-term reference image.

When at least one of the reference image of the current prediction unitand the reference image of the first candidate prediction unit is thelong-term reference image, the motion estimator 420 may determine toinclude the motion vector of the first candidate block in the candidatemotion vector list while a size of the motion vector of the firstcandidate block is not scaled, or may determine not to use the motionvector of the first candidate block in the candidate motion vector list.

The motion estimator 420 may determine a reference motion vector byselecting an optimal reference motion vector from among motion vectorsincluded in the candidate motion vector list and may predict anddetermine the motion vector of the current prediction unit by using theselected reference motion vector. The motion estimator 420 may determinea reference block that is indicated by the motion vector of the currentblock in the reference frame 495 of the current prediction unit and maygenerate residual data between the reference prediction unit and thecurrent prediction unit. Accordingly, the motion estimator 420 mayoutput residual data for each prediction unit.

Also, when the reference image of the first candidate prediction unitfrom among the candidate prediction units in the candidate motion vectorlist of the current prediction unit is different from the referenceframe 495 of the current prediction unit, the motion compensator 425 mayalso determine whether or not to use or whether to exclude the motionvector of the first candidate prediction unit from the candidate motionvector list, based on whether at least one of the reference frame 495 ofthe current prediction unit and the reference image of the firstcandidate prediction unit is the long-term reference image.

The motion compensator 425 may determine a reference motion vector byselecting an optimal reference motion vector from among the motionvectors included in the candidate motion vector list and may predict anddetermine the motion vector of the current prediction unit by using theselected reference motion vector.

The motion compensator 425 may determine a reference prediction unitthat is indicated by the motion vector of the current prediction unit inthe reference frame 495, may synthesize the reference prediction unitand the residual data of the current prediction unit, and thus mayrestore the current prediction unit.

Accordingly, the motion compensator 425 may perform motion compensationfor each prediction unit, may restore each prediction unit, and thus mayrestore the current image including the restored prediction units. Therestored prediction unit and image may become reference targets ofanother prediction unit and another image.

FIG. 13 is a block diagram of an image decoder 500 based on codingunits, according to an embodiment according to the present invention.

A parser 510 parses encoded image data to be decoded and informationabout encoding required for decoding from a bitstream 505. The encodedimage data is output as inverse quantized data through an entropydecoder 520 and an inverse quantizer 530, and the inverse quantized datais restored to image data in a spatial domain through an inversetransformer 540.

An intra predictor 550 performs intra prediction on coding units in anintra mode with respect to the image data in the spatial domain, and amotion compensator 560 performs motion compensation on coding units inan inter mode by using a reference frame 585.

The image data in the spatial domain, which passed through the intrapredictor 550 and the motion compensator 560, may be output as arestored frame 595 after being post-processed through a deblocking unit570 and a loop filtering unit 580. Also, the image data that ispost-processed through the deblocking unit 570 and the loop filteringunit 580 may be output as the reference frame 585.

In order to decode the image data in the image data decoder 230 of thevideo decoding apparatus 200, the image decoder 500 may performoperations that are performed after the parser 510 performs anoperation.

In order for the image decoder 500 to be applied in the video decodingapparatus 200, all elements of the image decoder 500, i.e., the parser510, the entropy decoder 520, the inverse quantizer 530, the inversetransformer 540, the intra predictor 550, the motion compensator 560,the deblocking unit 570, and the loop filtering unit 580 performoperations based on coding units having a tree structure for eachmaximum coding unit.

Specifically, the intra predictor 550 and the motion compensator 560perform operations based on partitions and a prediction mode for each ofthe coding units having a tree structure, and the inverse transformer540 perform operations based on a size of a transformation unit for eachcoding unit.

Specifically, when a reference image of a first candidate predictionunit from among candidate prediction units in a candidate motion vectorlist of a current prediction unit is different from the reference frame585 of the current prediction unit, the motion compensator 560 maydetermine whether or not to use or whether to exclude a motion vector ofthe first candidate prediction unit from the candidate motion vectorlist, based on whether at least one of the reference frame 585 of thecurrent prediction unit and the reference image of the first candidateprediction unit is a long-term reference image.

The motion compensator 560 may determine a reference motion vector byselecting an optimal reference motion vector from among the motionvectors included in the candidate motion vector list and may predict anddetermine the motion vector of the current prediction unit by using theselected reference motion vector.

The motion compensator 560 may determine the reference frame 585indicated by a POC according to the reference index of the currentprediction unit, may determine a reference prediction unit that isindicated by the motion vector of the current prediction unit in thereference frame 585, may synthesize the reference prediction unit andthe residual data of the current prediction unit, and thus may restorethe current prediction unit.

Accordingly, the motion compensator 560 may perform motion compensationfor each prediction unit, may restore each prediction unit, and thus mayrestore the current image including the restored prediction units. Therestored prediction unit and image may become reference targets ofanother prediction unit and another image.

FIG. 14 is a diagram illustrating deeper coding units according todepths, and partitions, according to an embodiment according to thepresent invention.

The video encoding apparatus 100 and the video decoding apparatus 200use hierarchical coding units so as to consider characteristics of animage. A maximum height, a maximum width, and a maximum depth of codingunits may be adaptively determined according to the characteristics ofthe image, or may be differently set by a user. Sizes of deeper codingunits according to depths may be determined according to thepredetermined maximum size of the coding unit.

In a hierarchical structure 600 of coding units, according to anembodiment according to the present invention, the maximum height andthe maximum width of the coding units are each 64, and the maximum depthis 4. In this case, the maximum depth refers to a total number of timesthe coding unit is split from the maximum coding unit to the minimumcoding unit. Since a depth deepens along a vertical axis of thehierarchical structure 600, a height and a width of the deeper codingunit are each split. Also, a prediction unit and partitions, which arebases for prediction encoding of each deeper coding unit, are shownalong a horizontal axis of the hierarchical structure 600.

In other words, a coding unit 610 is a maximum coding unit in thehierarchical structure 600, wherein a depth is 0 and a size, i.e., aheight by width, is 64×64. The depth deepens along the vertical axis,and a coding unit 620 having a size of 32×32 and a depth of 1, a codingunit 630 having a size of 16×16 and a depth of 2, and a coding unit 640having a size of 8×8 and a depth of 3 exist. The coding unit 640 havingthe size of 8×8 and the depth of 3 is a minimum coding unit having alowest depth.

The prediction unit and the partitions of a coding unit are arrangedalong the horizontal axis according to each depth. In other words, ifthe coding unit 610 having the size of 64×64 and the depth of 0 is aprediction unit, the prediction unit may be split into partitionsincluded in the encoding unit 610, i.e. a partition 610 having a size of64×64, partitions 612 having the size of 64×32, partitions 614 havingthe size of 32×64, or partitions 616 having the size of 32×32.

Similarly, a prediction unit of the coding unit 620 having the size of32×32 and the depth of 1 may be split into partitions included in thecoding unit 620, i.e. a partition 620 having a size of 32×32, partitions622 having a size of 32×16, partitions 624 having a size of 16×32, andpartitions 626 having a size of 16×16.

Similarly, a prediction unit of the coding unit 630 having the size of16×16 and the depth of 2 may be split into partitions included in thecoding unit 630, i.e. a partition having a size of 16×16 included in thecoding unit 630, partitions 632 having a size of 16×8, partitions 634having a size of 8×16, and partitions 636 having a size of 8×8.

Similarly, a prediction unit of the coding unit 640 having the size of8×8 and the depth of 3 may be split into partitions included in thecoding unit 640, i.e. a partition having a size of 8×8 included in thecoding unit 640, partitions 642 having a size of 8×4, partitions 644having a size of 4×8, and partitions 646 having a size of 4×4.

In order to determine the at least one coded depth of the coding unitsconstituting the maximum coding unit 610, the coding unit determiner 120of the video encoding apparatus 100 performs encoding for coding unitscorresponding to each depth included in the maximum coding unit 610.

A number of deeper coding units according to depths including data inthe same range and the same size increases as the depth deepens. Forexample, four coding units corresponding to a depth of 2 are required tocover data that is included in one coding unit corresponding to a depthof 1. Accordingly, in order to compare encoding results of the same dataaccording to depths, the coding unit corresponding to the depth of 1 andfour coding units corresponding to the depth of 2 are each encoded.

In order to perform encoding for a current depth from among the depths,a least encoding error may be selected for the current depth byperforming encoding for each prediction unit in the coding unitscorresponding to the current depth, along the horizontal axis of thehierarchical structure 600. Alternatively, the minimum encoding errormay be searched for by comparing the least encoding errors according todepths, by performing encoding for each depth as the depth deepens alongthe vertical axis of the hierarchical structure 600. A depth and apartition having the minimum encoding error in the coding unit 610 maybe selected as the coded depth and a partition type of the coding unit610.

FIG. 15 is a diagram for describing a relationship between a coding unit710 and transformation units 720, according to an embodiment accordingto the present invention.

The video encoding apparatus 100 or 200 encodes or decodes an imageaccording to coding units having sizes smaller than or equal to amaximum coding unit for each maximum coding unit. Sizes oftransformation units for transformation during encoding may be selectedbased on data units that are not larger than a corresponding codingunit.

For example, in the video encoding apparatus 100 or 200, if a size ofthe coding unit 710 is 64×64, transformation may be performed by usingthe transformation units 720 having a size of 32×32.

Also, data of the coding unit 710 having the size of 64×64 may beencoded by performing the transformation on each of the transformationunits having the size of 32×32, 16×16, 8×8, and 4×4, which are smallerthan 64×64, and then a transformation unit having the least coding errormay be selected.

FIG. 16 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an embodiment according tothe present invention.

The output unit 130 of the video encoding apparatus 100 may encode andtransmit information 800 about a partition type, information 810 about aprediction mode, and information 820 about a size of a transformationunit for each coding unit corresponding to a coded depth, as informationabout an encoding mode.

The information 800 indicates information about a shape of a partitionobtained by splitting a prediction unit of a current coding unit,wherein the partition is a data unit for prediction encoding the currentcoding unit. For example, a current coding unit CU_0 having a size of2N×2N may be split into any one of a partition 802 having a size of2N×2N, a partition 804 having a size of 2N×N, a partition 806 having asize of N×2N, and a partition 808 having a size of N×N. Here, theinformation 800 about a partition type is set to indicate one of thepartition 804 having a size of 2N×N, the partition 806 having a size ofN×2N, and the partition 808 having a size of N×N

The information 810 indicates a prediction mode of each partition. Forexample, the information 810 may indicate a mode of prediction encodingperformed on a partition indicated by the information 800, i.e., anintra mode 812, an inter mode 814, or a skip mode 816.

The information 820 indicates a transformation unit to be based on whentransformation is performed on a current coding unit. For example, thetransformation unit may be a first intra transformation unit 822, asecond intra transformation unit 824, a first inter transformation unit826, or a second inter transformation unit 828.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information 800, 810, and820 for decoding, according to each deeper coding unit.

FIG. 17 is a diagram of deeper coding units according to depths,according to an embodiment according to the present invention.

Split information may be used to indicate a change of a depth. The spiltinformation indicates whether a coding unit of a current depth is splitinto coding units of a lower depth.

A prediction unit 910 for prediction encoding a coding unit 900 having adepth of 0 and a size of 2N_0×2N_0 may include partitions of a partitiontype 912 having a size of 2N_0×2N_0, a partition type 914 having a sizeof 2N_0×N_0, a partition type 916 having a size of N_0×2N_0, and apartition type 918 having a size of N_0×N_0. FIG. 17 only illustratesthe partition types 912 through 918 which are obtained by symmetricallysplitting the prediction unit 910, but a partition type is not limitedthereto, and the partitions of the prediction unit 910 may includeasymmetrical partitions, partitions having a predetermined shape, andpartitions having a geometrical shape.

Prediction encoding is repeatedly performed on one partition having asize of 2N_0×2N_0, two partitions having a size of 2N_0×N_0, twopartitions having a size of N_0×2N_0, and four partitions having a sizeof N_0×N_0, according to each partition type. The prediction encoding inan intra mode and an inter mode may be performed on the partitionshaving the sizes of 2N_0×2N_0, N_0×2N_0, 2N_0×N_0, and N_0×N_0. Theprediction encoding in a skip mode is performed only on the partitionhaving the size of 2N_0×2N_0.

Errors of encoding including the prediction encoding in the partitiontypes 912 through 918 are compared, and the least encoding error isdetermined among the partition types. If an encoding error is smallestin one of the partition types 912 through 916, the prediction unit 910may not be split into a lower depth.

If the encoding error is the smallest in the partition type 918, a depthis changed from 0 to 1 to split the partition type 918 in operation 920,and encoding is repeatedly performed on coding units 930 having a depthof 2 and a size of N_0×N_0 to search for a minimum encoding error.

A prediction unit 940 for prediction encoding the coding unit 930 havinga depth of 1 and a size of 2N_1×2N_1 (=N_0×N_0) may include partitionsof a partition type 942 having a size of 2N_1×2N_1, a partition type 944having a size of 2N_1×N_1, a partition type 946 having a size ofN_1×2N_1, and a partition type 948 having a size of N_1×N_1.

If an encoding error is the smallest in the partition type 948, a depthis changed from 1 to 2 to split the partition type 948 in operation 950,and encoding is repeatedly performed on coding units 960, which have adepth of 2 and a size of N_2×N_2 to search for a minimum encoding error.

When a maximum depth is d, split operation according to each depth maybe performed up to when a depth becomes d−1, and split information maybe encoded as up to when a depth is one of 0 to d−2. In other words,when encoding is performed up to when the depth is d−1 after a codingunit corresponding to a depth of d−2 is split in operation 970, aprediction unit 990 for prediction encoding a coding unit 980 having adepth of d−1 and a size of 2N_(d−1)×2N_(d−1) may include partitions of apartition type 992 having a size of 2N_(d−1)×2N_(d−1), a partition type994 having a size of 2N_(d−1)×N_(d−1), a partition type 996 having asize of N_(d−1)×2N_(d−1), and a partition type 998 having a size ofN_(d−1)×N_(d−1). Prediction encoding may be repeatedly performed on onepartition having a size of 2N_(d−1)×2N_(d−1), two partitions having asize of 2N_(d−1)×N_(d−1), two partitions having a size ofN_(d−1)×2N_(d−1), four partitions having a size of N_(d−1)×N_(d−1) fromamong the partition types 992 through 998 to search for a partition typehaving a minimum encoding error.

Even when the partition type 998 has the minimum encoding error, since amaximum depth is d, a coding unit CU_(d−1) having a depth of d−1 is nolonger split to a lower depth, and a coded depth for the coding unitsconstituting a current maximum coding unit 900 is determined to be d−1and a partition type of the current maximum coding unit 900 may bedetermined to be N_(d−1)×N_(d−1). Also, since the maximum depth is d anda minimum coding unit 980 having a lowermost depth of d−1 is no longersplit to a lower depth, split information for the minimum coding unit980 is not set.

A data unit 999 may be a ‘minimum unit’ for the current maximum codingunit. A minimum unit according to an embodiment according to the presentinvention may be a rectangular data unit obtained by splitting a minimumcoding unit 980 by 4. By performing the encoding repeatedly, the videoencoding apparatus 100 may select a depth having the least encodingerror by comparing encoding errors according to depths of the codingunit 900 to determine a coded depth, and set a corresponding partitiontype and a prediction mode as an encoding mode of the coded depth. Assuch, the minimum encoding errors according to depths are compared inall of the depths of 1 through d, and a depth having the least encodingerror may be determined as a coded depth. The coded depth, the partitiontype of the prediction unit, and the prediction mode may be encoded andtransmitted as information about an encoding mode. Also, since a codingunit is split from a depth of 0 to a coded depth, only split informationof the coded depth is set to 0, and split information of depthsexcluding the coded depth is set to 1.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information about thecoded depth and the prediction unit of the coding unit 900 to decode thepartition 912. The video decoding apparatus 200 may determine a depth,in which split information is 0, as a coded depth by using splitinformation according to depths, and use information about an encodingmode of the corresponding depth for decoding.

FIGS. 18 through 20 are diagrams for describing a relationship betweencoding units 1010, prediction units 1060, and transformation units 1070,according to an embodiment according to the present invention.

The coding units 1010 are coding units having a tree structure,corresponding to coded depths determined by the video encoding apparatus100, in a maximum coding unit. The prediction units 1060 are partitionsof prediction units of each of the coding units 1010, and thetransformation units 1070 are transformation units of each of the codingunits 1010.

When a depth of a maximum coding unit is 0 in the coding units 1010,depths of coding units 1012 and 1054 are 1, depths of coding units 1014,1016, 1018, 1028, 1050, and 1052 are 2, depths of coding units 1020,1022, 1024, 1026, 1030, 1032, and 1048 are 3, and depths of coding units1040, 1042, 1044, and 1046 are 4.

In the prediction units 1060, some encoding units 1014, 1016, 1022,1032, 1048, 1050, 1052, and 1054 are obtained by splitting the codingunits in the encoding units 1010. In other words, partition types in thecoding units 1014, 1022, 1050, and 1054 have a size of 2N×N, partitiontypes in the coding units 1016, 1048, and 1052 have a size of N×2N, anda partition type of the coding unit 1032 has a size of N×N. Predictionunits and partitions of the coding units 1010 are smaller than or equalto each coding unit.

Transformation or inverse transformation is performed on image data ofthe coding unit 1052 in the transformation units 1070 in a data unitthat is smaller than the coding unit 1052. Also, the coding units 1014,1016, 1022, 1032, 1048, 1050, and 1052 in the transformation units 1070are different from those in the prediction units 1060 in terms of sizesand shapes. In other words, the video encoding and decoding apparatuses100 and 200 may perform intra prediction, motion estimation, motioncompensation, transformation, and inverse transformation individually ona data unit in the same coding unit.

Accordingly, encoding is recursively performed on each of coding unitshaving a hierarchical structure in each region of a maximum coding unitto determine an optimum coding unit, and thus coding units having arecursive tree structure may be obtained. Encoding information mayinclude split information about a coding unit, information about apartition type, information about a prediction mode, and informationabout a size of a transformation unit. Table 1 shows the encodinginformation that may be set by the video encoding and decodingapparatuses 100 and 200.

TABLE 1 Split Split Information 0 Information (Encoding on Coding Unithaving Size of 2N × 2N and Current Depth of d) 1 Prediction PartitionType Size of Transformation Unit Repeatedly Mode Encode IntraSymmetrical Asymmetrical Split Split Coding Inter Partition PartitionInformation 0 Information 1 Units Skip Type Type of of having (OnlyTransformation Transformation Lower 2N × 2N) Unit Unit Depth of 2N × 2N2N × nU 2N × 2N N × N d + 1 2N × N  2N × nD (Symmetrical  N × 2N nL × 2NType) N × N nR × 2N N/2 × N/2 (Asymmetrical Type)

The output unit 130 of the video encoding apparatus 100 may output theencoding information about the coding units having a tree structure, andthe image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract the encoding information about thecoding units having a tree structure from a received bitstream.

Split information indicates whether a current coding unit is split intocoding units of a lower depth. If split information of a current depth dis 0, a depth, in which a current coding unit is no longer split into alower depth, is a coded depth, and thus information about a partitiontype, prediction mode, and a size of a transformation unit may bedefined for the coded depth. If the current coding unit is further splitaccording to the split information, encoding is independently performedon four split coding units of a lower depth.

A prediction mode may be one of an intra mode, an inter mode, and a skipmode. The intra mode and the inter mode may be defined in all partitiontypes, and the skip mode is defined only in a partition type having asize of 2N×2N. The information about the partition type may indicatesymmetrical partition types having sizes of 2N×2N, 2N×N, N×2N, and N×N,which are obtained by symmetrically splitting a height or a width of aprediction unit, and asymmetrical partition types having sizes of 2N×nU,2N×nD, nL×2N, and nR×2N, which are obtained by asymmetrically splittingthe height or width of the prediction unit. The asymmetrical partitiontypes having the sizes of 2N×nU and 2N×nD may be respectively obtainedby splitting the height of the prediction unit in 1:3 and 3:1, and theasymmetrical partition types having the sizes of nL×2N and nR×2N may berespectively obtained by splitting the width of the prediction unit in1:3 and 3:1.

The size of the transformation unit may be set to be two types in theintra mode and two types in the inter mode. In other words, if splitinformation of the transformation unit is 0, the size of thetransformation unit may be 2N×2N, which is the size of the currentcoding unit. If split information of the transformation unit is 1, thetransformation units may be obtained by splitting the current codingunit. Also, if a partition type of the current coding unit having thesize of 2N×2N is a symmetrical partition type, a size of atransformation unit may be N×N, and if the partition type of the currentcoding unit is an asymmetrical partition type, the size of thetransformation unit may be N/2×N/2.

The encoding information about coding units having a tree structure mayinclude at least one of a coding unit corresponding to a coded depth, aprediction unit, and a minimum unit. The coding unit corresponding tothe coded depth may include at least one of a prediction unit and aminimum unit containing the same encoding information.

Accordingly, it is determined whether adjacent data units are includedin the same coding unit corresponding to the coded depth by comparingencoding information of the adjacent data units. Also, a correspondingcoding unit corresponding to a coded depth is determined by usingencoding information of a data unit, and thus a distribution of codeddepths in a maximum coding unit may be determined.

Accordingly, if a current coding unit is predicted based on encodinginformation of adjacent data units, encoding information of data unitsin deeper coding units adjacent to the current coding unit may bedirectly referred to and used.

Alternatively, if a current coding unit is predicted based on encodinginformation of adjacent data units, data units adjacent to the currentcoding unit are searched using encoded information of the data units,and the searched adjacent coding units may be referred to for predictingthe current coding unit.

FIG. 21 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to encoding mode information of Table 1.

A maximum coding unit 1300 includes coding units 1302, 1304, 1306, 1312,1314, 1316, and 1318 of coded depths. Here, since the coding unit 1318is a coding unit of a coded depth, split information may be set to 0.Information about a partition type of the coding unit 1318 having a sizeof 2N×2N may be set to be one of a partition type 1322 having a size of2N×2N, a partition type 1324 having a size of 2N×N, a partition type1326 having a size of N×2N, a partition type 1328 having a size of N×N,a partition type 1332 having a size of 2N×nU, a partition type 1334having a size of 2N×nD, a partition type 1336 having a size of nL×2N,and a partition type 1338 having a size of nR×2N.

Split information (TU (Transformation Unit)size flag) of atransformation unit is a type of a transformation index. The size of thetransformation unit corresponding to the transformation index may bechanged according to a prediction unit type or partition type of thecoding unit.

For example, when the partition type is set to be symmetrical, i.e. thepartition type 1322, 1324, 1326, or 1328, a transformation unit 1342having a size of 2N×2N is set if split information (TU size flag) of atransformation unit is 0, and a transformation unit 1344 having a sizeof N×N is set if a TU size flag is 1.

When the partition type is set to be asymmetrical, i.e., the partitiontype 1332, 1334, 1336, or 1338, a transformation unit 1352 having a sizeof 2N×2N is set if a TU size flag is 0, and a transformation unit 1354having a size of N/2×N/2 is set if a TU size flag is 1.

Referring to FIG. 21, the TU size flag is a flag having a value of 0 or1, but the TU size flag is not limited to 1 bit, and a transformationunit may be hierarchically split having a tree structure while the TUsize flag increases from 0. Split information (TU size flag) of atransformation unit may be an example of a transformation index.

In this case, the size of a transformation unit that has been actuallyused may be expressed by using a TU size flag of a transformation unit,according to an embodiment according to the present invention, togetherwith a maximum size and minimum size of the transformation unit.According to an embodiment according to the present invention, the videoencoding apparatus 100 is capable of encoding maximum transformationunit size information, minimum transformation unit size information, anda maximum TU size flag. The result of encoding the maximumtransformation unit size information, the minimum transformation unitsize information, and the maximum TU size flag may be inserted into anSPS. According to an embodiment according to the present invention, thevideo decoding apparatus 200 may decode video by using the maximumtransformation unit size information, the minimum transformation unitsize information, and the maximum TU size flag.

For example, (a) if the size of a current coding unit is 64×64 and amaximum transformation unit size is 32×32, (a−1) then the size of atransformation unit may be 32×32 when a TU size flag is 0, (a−2) may be16×16 when the TU size flag is 1, and (a−3) may be 8×8 when the TU sizeflag is 2.

As another example, (b) if the size of the current coding unit is 32×32and a minimum transformation unit size is 32×32, (b−1) then the size ofthe transformation unit may be 32×32 when the TU size flag is 0. Here,the TU size flag cannot be set to a value other than 0, since the sizeof the transformation unit cannot be less than 32×32.

As another example, (c) if the size of the current coding unit is 64×64and a maximum TU size flag is 1, then the TU size flag may be 0 or 1.Here, the TU size flag cannot be set to a value other than 0 or 1.

Thus, if it is defined that the maximum TU size flag is‘MaxTransformSizelndex’, a minimum transformation unit size is‘MinTransformSize’, and a transformation unit size is ‘RootTuSize’ whenthe TU size flag is 0, then a current minimum transformation unit size‘CurrMinTuSize’ that can be determined in a current coding unit, may bedefined by Equation (1):

CurrMinTuSize=max (MinTransformSize,RootTuSize/(2̂MaxTransformSizelndex))   (1)

Compared to the current minimum transformation unit size ‘CurrMinTuSize’that can be determined in the current coding unit, a transformation unitsize ‘RootTuSize’ when the TU size flag is 0 may denote a maximumtransformation unit size that can be selected in the system. In Equation(1), ‘RootTuSize/(2̂MaxTransformSizelndex)’ denotes a transformation unitsize when the transformation unit size ‘RootTuSize’, when the TU sizeflag is 0, is split a number of times corresponding to the maximum TUsize flag, and ‘MinTransformSize’ denotes a minimum transformation size.Thus, a smaller value from among ‘RootTuSize/(2̂MaxTransformSizelndex)’and ‘MinTransformSize’ may be the current minimum transformation unitsize ‘CurrMinTuSize’ that can be determined in the current coding unit.

According to an embodiment according to the present invention, themaximum transformation unit size RootTuSize may vary according to thetype of a prediction mode.

For example, if a current prediction mode is an inter mode, then‘RootTuSize’ may be determined by using Equation (2) below. In Equation(2), ‘MaxTransformSize’ denotes a maximum transformation unit size, and‘PUSize’ denotes a current prediction unit size.

RootTuSize=min(MaxTransformSize, PUSize)   (2)

That is, if the current prediction mode is the inter mode, thetransformation unit size ‘RootTuSize’, when the TU size flag is 0, maybe a smaller value from among the maximum transformation unit size andthe current prediction unit size.

If a prediction mode of a current partition unit is an intra mode,‘RootTuSize’ may be determined by using Equation (3) below. In Equation(3), ‘PartitionSize’ denotes the size of the current partition unit.

RootTuSize=min(MaxTransformSize, PartitionSize)   (3)

That is, if the current prediction mode is the intra mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0 may bea smaller value from among the maximum transformation unit size and thesize of the current partition unit. However, the current maximumtransformation unit size ‘RootTuSize’ that varies according to the typeof a prediction mode in a partition unit is just an example and thepresent invention is not limited thereto.

According to the video encoding method based on coding units having atree structure as described with reference to FIGS. 9 through 21, imagedata of a spatial region is encoded for each coding unit of a treestructure. According to the video decoding method based on coding unitshaving a tree structure, decoding is performed for each maximum codingunit to restore image data of a spatial region. Thus, a picture and avideo that is a picture sequence may be restored. The restored video maybe reproduced by a reproducing apparatus, stored in a storage medium, ortransmitted through a network.

The embodiments according to the present invention may be written ascomputer programs and may be implemented in general-use digitalcomputers that execute the programs using a computer readable recordingmedium. Examples of the computer readable recording medium includemagnetic storage media (e.g., ROM, floppy disks, hard disks, etc.) andoptical recording media (e.g., CD-ROMs, or DVDs).

For convenience of description, a video encoding method according to themotion vector determining method, which has been described withreference to FIGS. 1 through 21, will be collectively referred to as a‘video encoding method according to the present invention’. In addition,the video decoding method according to the motion vector determiningmethod, which has been described with reference to FIGS. 1 through 21,will be referred to as a ‘video decoding method according to the presentinvention’.

A video encoding apparatus including the motion vector determiningapparatus 10, the video encoding unit 70, the video decoding unit 80,and the video encoding apparatus 100, or the image encoder 400, whichhas been described with reference to FIGS. 1 through 21, will bereferred to as a ‘video encoding apparatus according to the presentinvention’. In addition, a video decoding apparatus including the motionvector determining apparatus 10, the video decoding unit 80, the videodecoding apparatus 200, or the image decoder 500, which has beendescried with reference to FIGS. 1 through 21, will be referred to as a‘video decoding apparatus according to the present invention’.

A computer readable recording medium storing a program, e.g., a disc26000, according to an embodiment of the present invention will now bedescribed in detail.

FIG. 22 illustrates a physical structure of a disc 26000 that stores aprogram, according to an embodiment of the present invention. The disc26000 which is a storage medium may be a hard drive, a compact disc-readonly memory (CD-ROM) disc, a Blu-ray disc, or a digital versatile disc(DVD). The disc 26000 includes a plurality of concentric tracks Tr eachbeing divided into a specific number of sectors Se in a circumferentialdirection of the disc 26000. In a specific region of the disc 26000, aprogram that executes the motion vector determining method, the videoencoding method, and the video decoding method as described above may beassigned and stored.

A computer system embodied using a storage medium that stores a programfor executing a video encoding method and a video decoding method asdescribed above will now be described with reference to FIG. 23.

FIG. 23 illustrates a disc drive 26800 that records and reads a programby using a disc 26000. A computer system 26700 may store a program thatexecutes at least one of a video encoding method and a video decodingmethod according to an embodiment of the present invention, in a disc26000 via the disc drive 26800. To run the program stored in the disc26000 in the computer system 26700, the program may be read from thedisc 26000 and be transmitted to the computer system 26700 by using thedisc drive 26800.

The program that executes at least one of a video encoding method and avideo decoding method according to an embodiment of the presentinvention may be stored not only in the disc 26000 illustrated in FIG.22 or 23 but also in a memory card, a ROM cassette, or a solid statedrive (SSD).

A system to which the video encoding method and a video decoding methoddescribed above are applied will be described below.

FIG. 24 illustrates an entire structure of a content supply system 11000that provides content distribution service. A service area of acommunication system is divided into predetermined-sized cells, andwireless base stations 11700, 11800, 11900, and 12000 are installed inthese cells, respectively.

The content supply system 11000 includes a plurality of independentdevices. For example, the plurality of independent devices, such as acomputer 12100, a personal digital assistant (PDA) 12200, a video camera12300, and a mobile phone 12500, are connected to the Internet 11100 viaan internet service provider 11200, a communication network 11400, andthe wireless base stations 11700, 11800, 11900, and 12000.

However, the content supply system 11000 is not limited to asillustrated in FIG. 24, and devices may be selectively connectedthereto. The plurality of independent devices may be directly connectedto the communication network 11400, not via the wireless base stations11700, 11800, 11900, and 12000.

The video camera 12300 is an imaging device, e.g., a digital videocamera, which is capable of capturing video images. The mobile phone12500 may employ at least one communication method from among variousprotocols, e.g., Personal Digital Communications (PDC), Code DivisionMultiple Access (CDMA), Wideband-Code Division Multiple Access (W-CDMA),Global System for Mobile Communications (GSM), and Personal HandyphoneSystem (PHS).

The video camera 12300 may be connected to a streaming server 11300 viathe wireless base station 11900 and the communication network 11400. Thestreaming server 11300 allows content received from a user via the videocamera 12300 to be streamed via a real-time broadcast. The contentreceived from the video camera 12300 may be encoded using the videocamera 12300 or the streaming server 11300. Video data captured by thevideo camera 12300 may be transmitted to the streaming server 11300 viathe computer 12100.

Video data captured by a camera 12600 may also be transmitted to thestreaming server 11300 via the computer 12100. The camera 12600 is animaging device capable of capturing both still images and video images,similar to a digital camera. The video data captured by the camera 12600may be encoded using the camera 12600 or the computer 12100. Softwarethat performs encoding and decoding video may be stored in a computerreadable recording medium, e.g., a CD-ROM disc, a floppy disc, a harddisc drive, an SSD, or a memory card, which may be accessible by thecomputer 12100.

If video data is captured by a camera built in the mobile phone 12500,the video data may be received from the mobile phone 12500.

The video data may also be encoded by a large scale integrated circuit(LSI) system installed in the video camera 12300, the mobile phone12500, or the camera 12600.

According to an embodiment of the present invention, the content supplysystem 11000 may encode content data recorded by a user using the videocamera 12300, the camera 12600, the mobile phone 12500, or anotherimaging device, e.g., content recorded during a concert, and transmitthe encoded content data to the streaming server 11300. The streamingserver 11300 may transmit the encoded content data in a type of astreaming content to other clients that request the content data.

The clients are devices capable of decoding the encoded content data,e.g., the computer 12100, the PDA 12200, the video camera 12300, or themobile phone 12500. Thus, the content supply system 11000 allows theclients to receive and reproduce the encoded content data. Also, thecontent supply system 11000 allows the clients to receive the encodedcontent data and decode and reproduce the encoded content data in realtime, thereby enabling personal broadcasting.

Encoding and decoding operations of the plurality of independent devicesincluded in the content supply system 11000 may be similar to those of avideo encoding apparatus and a video decoding apparatus according to anembodiment of the present invention.

The mobile phone 12500 included in the content supply system 11000according to an embodiment of the present invention will now bedescribed in greater detail with referring to FIGS. 25 and 26.

FIG. 25 illustrates an external structure of a mobile phone 12500 towhich a video encoding method and a video decoding method are applied,according to an embodiment of the present invention. The mobile phone12500 may be a smart phone, the functions of which are not limited and alarge part of the functions of which may be changed or expanded.

The mobile phone 12500 includes an internal antenna 12510 via which aradio-frequency (RF) signal may be exchanged with the wireless basestation 12000 of FIG. 25, and includes a display screen 12520 fordisplaying images captured by a camera 12530 or images that are receivedvia the antenna 12510 and decoded, e.g., a liquid crystal display (LCD)or an organic light-emitting diodes (OLED) screen. The smart phone 12500includes an operation panel 12540 including a control button and a touchpanel. If the display screen 12520 is a touch screen, the operationpanel 12540 further includes a touch sensing panel of the display screen12520. The smart phone 12500 includes a speaker 12580 for outputtingvoice and sound or another type sound output unit, and a microphone12550 for inputting voice and sound or another type sound input unit.The smart phone 12500 further includes the camera 12530, such as acharge-coupled device (CCD) camera, to capture video and still images.The smart phone 12500 may further include a storage medium 12570 forstoring encoded/decoded data, e.g., video or still images captured bythe camera 12530, received via email, or obtained according to variousways; and a slot 12560 via which the storage medium 12570 is loaded intothe mobile phone 12500. The storage medium 12570 may be a flash memory,e.g., a secure digital (SD) card or an electrically erasable andprogrammable read only memory (EEPROM) included in a plastic case.

FIG. 26 illustrates an internal structure of the mobile phone 12500,according to an embodiment of the present invention. To systemicallycontrol parts of the mobile phone 12500 including the display screen1252 and the operation panel 12540, a power supply circuit 12700, anoperation input controller 12640, an image encoding unit 12720, a camerainterface 12630, an LCD controller 12620, an image decoding unit 12690,a multiplexer/demultiplexer 12680, a recording/reading unit 12670, amodulation/demodulation unit 12660, and a sound processor 12650 areconnected to a central controller 12710 via a synchronization bus 12730.

If a user operates a power button and sets from a ‘power off’ state to apower on' state, the power supply circuit 12700 supplies power to allthe parts of the mobile phone 12500 from a battery pack, thereby settingthe mobile phone 12500 in an operation mode.

The central controller 12710 includes a central processing unit (CPU), aROM, and a random access memory (RAM).

While the mobile phone 12500 transmits communication data to theoutside, a digital signal is generated in the mobile phone 12500 undercontrol of the central controller. For example, the sound processor12650 may generate a digital sound signal, the image encoding unit 12720may generate a digital image signal, and text data of a message may begenerated via the operation panel 12540 and the operation inputcontroller 12640. When a digital signal is delivered to themodulation/demodulation unit 12660 under control of the centralcontroller 12710, the modulation/demodulation unit 12660 modulates afrequency band of the digital signal, and a communication circuit 12610performs digital-to-analog conversion (DAC) and frequency conversion onthe frequency band-modulated digital sound signal. A transmission signaloutput from the communication circuit 12610 may be transmitted to avoice communication base station or the wireless base station 12000 viathe antenna 12510.

For example, when the mobile phone 12500 is in a conversation mode, asound signal obtained via the microphone 12550 is transformed into adigital sound signal by the sound processor 12650, under control of thecentral controller 12710. The digital sound signal may be transformedinto a transformation signal via the modulation/demodulation unit 12660and the communication circuit 12610, and may be transmitted via theantenna 12510.

When a text message, e.g., email, is transmitted in a data communicationmode, text data of the text message is input via the operation panel12540 and is transmitted to the central controller 12610 via theoperation input controller 12640. Under control of the centralcontroller 12610, the text data is transformed into a transmissionsignal via the modulation/demodulation unit 12660 and the communicationcircuit 12610 and is transmitted to the wireless base station 12000 viathe antenna 12510.

To transmit image data in the data communication mode, image datacaptured by the camera 12530 is provided to the image encoding unit12720 via the camera interface 12630. The captured image data may bedirectly displayed on the display screen 12520 via the camera interface12630 and the LCD controller 12620.

A structure of the image encoding unit 12720 may correspond to that ofthe video encoding apparatus 100 described above. The image encodingunit 12720 may transform the image data received from the camera 12530into compressed and encoded image data according to a video encodingmethod employed by the video encoding apparatus 100 or the image encoder400 described above, and then output the encoded image data to themultiplexer/demultiplexer 12680. During a recording operation of thecamera 12530, a sound signal obtained by the microphone 12550 of themobile phone 12500 may be transformed into digital sound data via thesound processor 12650, and the digital sound data may be delivered tothe multiplexer/demultiplexer 12680.

The multiplexer/demultiplexer 12680 multiplexes the encoded image datareceived from the image encoding unit 12720, together with the sounddata received from the sound processor 12650. A result of multiplexingthe data may be transformed into a transmission signal via themodulation/demodulation unit 12660 and the communication circuit 12610,and may then be transmitted via the antenna 12510.

While the mobile phone 12500 receives communication data from theoutside, frequency recovery and ADC are performed on a signal receivedvia the antenna 12510 to transform the signal into a digital signal. Themodulation/demodulation unit 12660 modulates a frequency band of thedigital signal. The frequency-band modulated digital signal istransmitted to the video decoding unit 12690, the sound processor 12650,or the LCD controller 12620, according to the type of the digitalsignal.

In the conversation mode, the mobile phone 12500 amplifies a signalreceived via the antenna 12510, and obtains a digital sound signal byperforming frequency conversion and ADC on the amplified signal. Areceived digital sound signal is transformed into an analog sound signalvia the modulation/demodulation unit 12660 and the sound processor12650, and the analog sound signal is output via the speaker 12580,under control of the central controller 12710.

When in the data communication mode, data of a video file accessed at anInternet website is received, a signal received from wireless basestation 12000 via the antenna 12510 is output as multiplexed data viathe modulation/demodulation unit 12660, and the multiplexed data istransmitted to the multiplexer/demultiplexer 12680.

To decode the multiplexed data received via the antenna 12510, themultiplexer/demultiplexer 12680 demultiplexes the multiplexed data intoan encoded video data stream and an encoded audio data stream. Via thesynchronization bus 12730, the encoded video data stream and the encodedaudio data stream are provided to the video decoding unit 12690 and thesound processor 12650, respectively.

A structure of the image decoding unit 12690 may correspond to that ofthe video decoding apparatus 200 described above. The image decodingunit 12690 may decode the encoded video data to obtain restored videodata and provide the restored video data to the display screen 12520 viathe LCD controller 12620, according to a video decoding method employedby the video decoding apparatus 200 or the image decoder 500 describedabove.

Thus, the data of the video file accessed at the Internet website may bedisplayed on the display screen 12520. At the same time, the soundprocessor 12650 may transform audio data into an analog sound signal,and provide the analog sound signal to the speaker 12580. Thus, audiodata contained in the video file accessed at the Internet website mayalso be reproduced via the speaker 12580.

The mobile phone 12500 or another type of communication terminal may bea transceiving terminal including both a video encoding apparatus and avideo decoding apparatus according to an embodiment of the presentinvention, may be a transceiving terminal including only the videoencoding apparatus, or may be a transceiving terminal including only thevideo decoding apparatus.

A communication system according to the present invention is not limitedto the communication system described above with reference to FIG. 25.For example, FIG. 27 illustrates a digital broadcasting system employinga communication system, according to an embodiment of the presentinvention. The digital broadcasting system of FIG. 27 may receive adigital broadcast transmitted via a satellite or a terrestrial networkby using a video encoding apparatus and a video decoding apparatusaccording to an embodiment of the present invention.

Specifically, a broadcasting station 12890 transmits a video data streamto a communication satellite or a broadcasting satellite 12900 by usingradio waves. The broadcasting satellite 12900 transmits a broadcastsignal, and the broadcast signal is transmitted to a satellite broadcastreceiver via a household antenna 12860. In every house, an encoded videostream may be decoded and reproduced by a TV receiver 12810, a set-topbox 12870, or another device.

When a video decoding apparatus according to an embodiment of thepresent invention is implemented in a reproducing apparatus 12830, thereproducing apparatus 12830 may parse and decode an encoded video streamrecorded on a storage medium 12820, such as a disc or a memory card torestore digital signals. Thus, the restored video signal may bereproduced, for example, on a monitor 12840.

In the set-top box 12870 connected to the antenna 12860 for asatellite/terrestrial broadcast or a cable antenna 12850 for receiving acable television (TV) broadcast, a video decoding apparatus according toan embodiment of the present invention may be installed. Data outputfrom the set-top box 12870 may also be reproduced on a TV monitor 12880.

As another example, a video decoding apparatus according to anembodiment of the present invention may be installed in the TV receiver12810 instead of the set-top box 12870.

An automobile 12920 including an appropriate antenna 12910 may receive asignal transmitted from the satellite 12900 or the wireless base station11700. A decoded video may be reproduced on a display screen of anautomobile navigation system 12930 built in the automobile 12920.

A video signal may be encoded by a video encoding apparatus according toan embodiment of the present invention and may then be stored in astorage medium. Specifically, an image signal may be stored in a DVDdisc 12960 by a DVD recorder or may be stored in a hard disc by a harddisc recorder 12950. As another example, the video signal may be storedin an SD card 12970. If the hard disc recorder 12950 includes a videodecoding apparatus according to an embodiment of the present invention,a video signal recorded on the DVD disc 12960, the SD card 12970, oranother storage medium may be reproduced on the TV monitor 12880.

The automobile navigation system 12930 may not include the camera 12530,the camera interface 12630, and the image encoding unit 12720 of FIG.27. For example, the computer 12100 and the TV receiver 12810 may not beincluded in the camera 12530, the camera interface 12630, and the imageencoding unit 12720 of FIG. 27.

FIG. 28 illustrates a network structure of a cloud computing systemusing a video encoding apparatus and a video decoding apparatus,according to an embodiment of the present invention.

The cloud computing system may include a cloud computing server 14000, auser database (DB) 14100, a plurality of computing resources 14200, anda user terminal.

The cloud computing system provides an on-demand outsourcing service ofthe plurality of computing resources 14200 via a data communicationnetwork, e.g., the Internet, in response to a request from the userterminal. Under a cloud computing environment, a service providerprovides users with desired services by combining computing resources atdata centers located at physically different locations by usingvirtualization technology. A service user does not have to installcomputing resources, e.g., an application, a storage, an operatingsystem (OS), and security, into his/her own terminal in order to usethem, but may select and use desired services from among services in avirtual space generated through the virtualization technology, at adesired point of time.

A user terminal of a specified service user is connected to the cloudcomputing server 14100 via a data communication network including theInternet and a mobile telecommunication network. User terminals may beprovided cloud computing services, and particularly video reproductionservices, from the cloud computing server 14100. The user terminals maybe various types of electronic devices capable of being connected to theInternet, e.g., a desk-top PC 14300, a smart TV 14400, a smart phone14500, a notebook computer 14600, a portable multimedia player (PMP)14700, a tablet PC 14800, and the like.

The cloud computing server 14100 may combine the plurality of computingresources 14200 distributed in a cloud network and provide userterminals with a result of the combining. The plurality of computingresources 14200 may include various data services, and may include datauploaded from user terminals. As described above, the cloud computingserver 14100 may provide user terminals with desired services bycombining video database distributed in different regions according tothe virtualization technology.

User information about users who has subscribed to a cloud computingservice is stored in the user DB 14100. The user information may includelogging information, addresses, names, and personal credit informationof the users. The user information may further include indexes ofvideos. Here, the indexes may include a list of videos that have alreadybeen reproduced, a list of videos that are being reproduced, a pausingpoint of a video that was being reproduced, and the like.

Information about a video stored in the user DB 14100 may be sharedbetween user devices. For example, when a video service is provided tothe notebook computer 14600 in response to a request from the notebookcomputer 14600, a reproduction history of the video service is stored inthe user DB 14100. When a request to reproduce this video service isreceived from the smart phone 14500, the cloud computing server 14100searches for and reproduces this video service, based on the user DB14100. When the smart phone 14500 receives a video data stream from thecloud computing server 14100, a process of reproducing video by decodingthe video data stream is similar to an operation of the mobile phone12500 described above with reference to FIG. 27.

The cloud computing server 14100 may refer to a reproduction history ofa desired video service, stored in the user DB 14100. For example, thecloud computing server 14100 receives a request to reproduce a videostored in the user DB 14100, from a user terminal. If this video wasbeing reproduced, then a method of streaming this video, performed bythe cloud computing server 14100 may vary according to the request fromthe user terminal, i.e., according to whether the video will bereproduced, starting from a start thereof or a pausing point thereof.For example, if the user terminal requests to reproduce the video,starting from the start thereof, the cloud computing server 14100transmits streaming data of the video starting from a first framethereof to the user terminal. If the user terminal requests to reproducethe video, starting from the pausing point thereof, the cloud computingserver 14100 transmits streaming data of the video starting from a framecorresponding to the pausing point, to the user terminal.

In this case, the user terminal may include a video decoding apparatusas described above with reference to FIGS. 1 to 23. As another example,the user terminal may include a video encoding apparatus as describedabove with reference to FIGS. 1 to 23. Alternatively, the user terminalmay include both the video decoding apparatus and the video encodingapparatus as described above with reference to FIGS. 1 to 23.

Various applications of a video encoding method, a video decodingmethod, a video encoding apparatus, and a video decoding apparatusaccording to embodiments of the present invention described above withreference to FIGS. 1 to 21 have been described above with reference toFIGS. 22 to 28. However, methods of storing the video encoding methodand the video decoding method in a storage medium or methods ofimplementing the video encoding apparatus and the video decodingapparatus in a device according to various embodiments of the presentinvention, are not limited to the embodiments described above withreference to FIGS. 22 to 28.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeaccording to the present invention as defined by the following claims.

1. An apparatus for encoding an image, the apparatus comprising: atleast one processor configured to: when a reference image of a firstcandidate block from among a plurality of candidate blocks adjacent to acurrent block, is different from a reference image of the current block,determine whether each of the reference image of the current block andthe reference image of the first candidate block is a short-termreference image or a long-term reference image; obtain long-termreference information indicating whether the reference image of thecurrent block is a long-term reference image; when one of the referenceimage of the first candidate block and the reference image of thecurrent block is the long-term reference image and the other one of thereference image of the first candidate block and the reference image ofthe current block is the short-term reference image, determine a motionvector of the first candidate block as being un-available; and when bothof the reference image of the first candidate block and the referenceimage of the current block are short-term reference images, determinedifference information based on scaling of the motion vector of thefirst candidate block and on a motion vector of the current block.
 2. Anon-transitory computer-readable storage medium having embodied thereoncomputer-readable codes, which when executed by a processor of anencoder causes the encoder to execute a method of encoding an image, themethod comprising: when a reference image of a first candidate blockfrom among a plurality of candidate blocks adjacent to a current block,is different from a reference image of the current block, determiningwhether each of the reference image of the current block and thereference image of the first candidate block is a short-term referenceimage or a long-term reference image; obtaining long-term referenceinformation indicating whether the reference image of the current blockis a long-term reference image; when one of the reference image of thefirst candidate block and the reference image of the current block isthe long-term reference image and the other one of the reference imageof the first candidate block and the reference image of the currentblock is the short-term reference image, determining a motion vector ofthe first candidate block as being un-available; when both of thereference image of the first candidate block and the reference image ofthe current block are short-term reference images, determiningdifference information based on scaling of the motion vector of thefirst candidate block and on a motion vector of the current block; andgenerating a bitstream comprising the long-term reference informationand the difference information.
 3. A method of encoding an image, themethod comprising: determining whether a reference picture of a currentblock is equal to a reference picture of a candidate block from among aplurality of candidate blocks adjacent to the current block; obtainingan index indicating the reference picture of the current block; when thereference picture of the candidate block is not equal to the referencepicture of the current block, determining whether each of the referencepicture of the candidate block and the reference picture of the currentblock is a long-term reference picture; obtaining long-term referenceinformation indicating whether the reference picture of the currentblock is a long-term reference picture; when one of the referencepicture of the candidate block and the reference picture of the currentblock is the long-term reference picture and the other one of thereference picture of the candidate block and the reference picture ofthe current block is a short-term reference picture, determining that amotion vector of the candidate block is un-available; when both of thereference picture of the current block and the reference picture of thecandidate block are short-term reference pictures, obtaining a spatialmotion vector prediction candidate by scaling the motion vector of thecandidate block; and determining difference information by using thespatial motion vector prediction candidate and a motion vector of thecurrent block.
 4. A non-transitory computer-readable storage mediumhaving embodied thereon computer-readable codes, which when executed bya processor of an encoder causes the encoder to execute a method ofencoding an image, the method comprising: determining whether areference picture of a current block is equal to a reference picture ofa candidate block from among a plurality of candidate blocks adjacent tothe current block; obtaining an index indicating the reference pictureof the current block; when the reference picture of the candidate blockis not equal to the reference picture of the current block, determiningwhether each of the reference picture of the candidate block and thereference picture of the current block is a long-term reference picture;obtaining long-term reference information indicating whether thereference picture of the current block is a long-term reference picture;when one of the reference picture of the candidate block and thereference picture of the current block is the long-term referencepicture and the other one of the reference picture of the candidateblock and the reference picture of the current block is a short-termreference picture, determining that a motion vector of the candidateblock is un-available; when both of the reference picture of the currentblock and the reference picture of the candidate block are short-termreference pictures, obtaining a spatial motion vector predictioncandidate by scaling the motion vector of the candidate block;determining difference information by using the spatial motion vectorprediction candidate and a motion vector of the current block; andgenerating a bitstream comprising the index indicating the referencepicture of the current block, the long-term reference information andthe difference information.
 5. An apparatus for encoding an image, theapparatus comprising: at least one processor configured to: determinewhether a reference picture of a current block is equal to a referencepicture of a candidate block from among a plurality of candidate blocksadjacent to the current block; obtain an index indicating the referencepicture of the current block; when the reference picture of thecandidate block is not equal to the reference picture of the currentblock, determine whether each of the reference picture of the candidateblock and the reference picture of the current block is a long-termreference picture; obtaining long-term reference information indicatingwhether the reference picture of the current block is a long-termreference picture; when one of the reference picture of the candidateblock and the reference picture of the current block is the long-termreference picture and the other one of the reference picture of thecandidate block and the reference picture of the current block is ashort-term reference picture, determine that a motion vector of thecandidate block is un-available; when both of the reference picture ofthe current block and the reference picture of the candidate block areshort-term reference pictures, obtain a spatial motion vector predictioncandidate by scaling the motion vector of the candidate block; anddetermine difference information by using the motion vector of thecandidate block and a motion vector of the current block.
 6. Anapparatus for encoding an image, the apparatus comprising: at least oneprocessor configured to: when a reference picture of a candidate blockand a reference picture of a current block are different, determinewhether each of the reference picture of the candidate block and thereference picture of the current block is a long-term reference picture,wherein the candidate block is from among a plurality of candidateblocks adjacent to the current block; obtain long-term referenceinformation indicating whether the reference picture of the currentblock is a long-term reference picture; when one of the referencepicture of the candidate block and the reference picture of the currentblock is a long-term reference picture and the other one of thereference picture of the candidate block and the reference picture ofthe current block is a short-term reference picture, determine that amotion vector of the candidate block is un-available; when both of thereference picture of the current block and the reference picture of thecandidate block are short-term reference pictures, obtain a motionvector prediction candidate by scaling the motion vector of thecandidate block; and determine difference information by using themotion vector prediction candidate and a motion vector of the currentblock.
 7. A non-transitory computer-readable storage medium havingembodied thereon computer-readable codes, which when executed by aprocessor of an encoder causes the encoder to execute a method ofencoding an image, the method comprising: when a reference picture of acandidate block and a reference picture of a current block aredifferent, determining whether each of the reference picture of thecandidate block and the reference picture of the current block is along-term reference picture, wherein the candidate block is from among aplurality of candidate blocks adjacent to the current block; obtaininglong-term reference information indicating whether the reference pictureof the current block is a long-term reference picture; when one of thereference picture of the candidate block and the reference picture ofthe current block is a long-term reference picture and the other one ofthe reference picture of the candidate block and the reference pictureof the current block is a short-term reference picture, determining thata motion vector of the candidate block is un-available; when both of thereference picture of the current block and the reference picture of thecandidate block are short-term reference pictures, obtaining a motionvector prediction candidate by scaling the motion vector of thecandidate block; determining difference information by using the motionvector prediction candidate and a motion vector of the current block;and generating a bitstream comprising the long-term referenceinformation and the difference information.
 8. A method of encoding animage, the method comprising: determining a plurality of maximum codingunits by splitting an image; generating split information used tohierarchically split a maximum coding unit, among the plurality ofmaximum coding units, into coding units of depth including at least oneof a current depth and a lower depth; when a reference image of acandidate block and a reference image of a current prediction unit aredifferent, determining whether each of the reference image of thecandidate block and the reference image of the current prediction unitis a long-term reference image, wherein the candidate block is fromamong a plurality of candidate blocks adjacent to the current predictionunit; obtaining long-term reference information indicating whether thereference image of the current prediction unit is a long-term referenceimage; when both of the reference image of the candidate block and thereference image of the current prediction unit are the long-termreference images, obtaining a motion vector prediction candidate withoutscaling a motion vector of the candidate block; and determiningdifference information by using the motion vector prediction candidateand a motion vector of the current prediction unit. wherein, when one ormore prediction units that comprise the current prediction unit areobtained from a coding unit of the current depth, the split informationindicates a non-split of the current depth.
 9. A non-transitorycomputer-readable storage medium having embodied thereoncomputer-readable codes, which when executed by a processor of anencoder causes the encoder to execute a method of encoding an image, themethod comprising: determining a plurality of maximum coding units bysplitting an image; generating split information used to hierarchicallysplit a maximum coding unit, among the plurality of maximum codingunits, into coding units of depth including at least one of a currentdepth and a lower depth; when a reference image of a candidate block anda reference image of a current prediction unit are different,determining whether each of the reference image of the candidate blockand the reference image of the current prediction unit is a long-termreference image, wherein the candidate block is from among a pluralityof candidate blocks adjacent to the current prediction unit; obtaininglong-term reference information indicating whether the reference imageof the current prediction unit is a long-term reference image; when bothof the reference image of the candidate block and the reference image ofthe current prediction unit are the long-term reference images,obtaining a motion vector prediction candidate without scaling a motionvector of the candidate block; determining difference information byusing the motion vector prediction candidate and a motion vector of thecurrent prediction unit; and generating a bitstream comprising the splitinformation, the long-term reference information and the differenceinformation, wherein, when one or more prediction units that comprisethe current prediction unit are obtained from a coding unit of thecurrent depth, the split information indicates a non-split of thecurrent depth.
 10. A non-transitory computer-readable storage mediumhaving embodied thereon computer-readable codes, which when executed bya processor of an encoder causes the encoder to execute a method ofencoding an image, the method comprising: determining a plurality ofmaximum coding units by splitting an image; generating split informationused to hierarchically split a maximum coding unit, among the pluralityof maximum coding units, into coding units of depth including at leastone of a current depth and a lower depth; determining whether areference picture of a current block is equal to a reference picture ofa candidate block from among a plurality of candidate blocks adjacent tothe current block; obtaining an index indicating the reference pictureof the current block; when the reference picture of the candidate blockis not equal to the reference picture of the current block, determiningwhether each of the reference picture of the candidate block and thereference picture of the current block is a long-term reference picture;obtaining long-term reference information indicating whether thereference picture of the current block is a long-term reference picture;when one of the reference picture of the candidate block and thereference picture of the current block is the long-term referencepicture and the other one of the reference picture of the candidateblock and the reference picture of the current block is a short-termreference picture, determining that a motion vector of the candidateblock is un-available; when both of the reference picture of the currentblock and the reference picture of the candidate block are short-termreference pictures, obtaining a spatial motion vector predictioncandidate by scaling the motion vector of the candidate block;determining difference information by using the spatial motion vectorprediction candidate and a motion vector of the current block; andgenerating a bitstream comprising the split information, the indexindicating the reference picture of the current block, the long-termreference information and the difference information, wherein, when oneor more prediction units that comprise the current block are obtainedfrom a coding unit of the current depth, the split information indicatesa non-split of the current depth.